Our applications, built on Elasticsearch[0], frequently create and
delete files. These applications operate within containers, some with a
memory limit exceeding 100GB. Over prolonged periods, the accumulation
of negative dentries within these containers can amount to tens of
gigabytes.
Upon container exit, directories are deleted. However, due to the
numerous associated dentries, this process can be time-consuming. Our
users have expressed frustration with this prolonged exit duration,
which constitutes our first issue.
Simultaneously, other processes may attempt to access the parent
directory of the Elasticsearch directories. Since the task responsible
for deleting the dentries holds the inode lock, processes attempting
directory lookup experience significant delays. This issue, our second
problem, is easily demonstrated:
- Task 1 generates negative dentries:
$ pwd
~/test
$ mkdir es && cd es/ && ./create_and_delete_files.sh
[ After generating tens of GB dentries ]
$ cd ~/test && rm -rf es
[ It will take a long duration to finish ]
- Task 2 attempts to lookup the 'test/' directory
$ pwd
~/test
$ ls
The 'ls' command in Task 2 experiences prolonged execution as Task 1
is deleting the dentries.
We've devised a solution to address both issues by deleting associated
dentry when removing a file. Interestingly, we've noted that a similar
patch was proposed years ago[1], although it was rejected citing the
absence of tangible issues caused by negative dentries. Given our
current challenges, we're resubmitting the proposal. All relevant
stakeholders from previous discussions have been included for reference.
Some alternative solutions are also under discussion[2][3], such as
shrinking child dentries outside of the parent inode lock or even
asynchronously shrinking child dentries. However, given the
straightforward nature of the current solution, I believe this approach
is still necessary.
[ NOTE! This is a pretty fundamental change in how we deal with
unlinking dentries, and it doesn't change the fact that you can have
lots of negative dentries from just doing negative lookups.
But the kernel test robot is at least initially happy with this from a
performance angle, so I'm applying this ASAP just to get more testing
and as a "known fix for an issue people hit in real life".
Put another way: we should still look at the alternatives, and this
patch may get reverted if somebody finds a performance regression on
some other load. - Linus ]
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://github.com/elastic/elasticsearch [0]
Link: https://patchwork.kernel.org/project/linux-fsdevel/patch/1502099673-31620-1-git-send-email-wangkai86@huawei.com [1]
Link: https://lore.kernel.org/linux-fsdevel/20240511200240.6354-2-torvalds@linux-foundation.org/ [2]
Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wjEMf8Du4UFzxuToGDnF3yLaMcrYeyNAaH1NJWa6fwcNQ@mail.gmail.com/ [3]
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Wangkai <wangkai86@huawei.com>
Cc: Colin Walters <walters@verbum.org>
Tested-by: kernel test robot <oliver.sang@intel.com>
Link: https://lore.kernel.org/all/202405221518.ecea2810-oliver.sang@intel.com/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently, the __d_clear_type_and_inode() writes the value flags to
dentry->d_flags, then immediately re-reads it in order to use it in a if
statement. This re-read is useless because no other update to
dentry->d_flags can occur at this point.
This commit therefore re-use flags in the if statement instead of
re-reading dentry->d_flags.
Signed-off-by: linke li <lilinke99@qq.com>
Link: https://lore.kernel.org/r/tencent_5E187BD0A61BA28605E85405F15228254D0A@qq.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'vfs-6.9.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs
Pull misc vfs updates from Christian Brauner:
"Misc features, cleanups, and fixes for vfs and individual filesystems.
Features:
- Support idmapped mounts for hugetlbfs.
- Add RWF_NOAPPEND flag for pwritev2(). This allows us to fix a bug
where the passed offset is ignored if the file is O_APPEND. The new
flag allows a caller to enforce that the offset is honored to
conform to posix even if the file was opened in append mode.
- Move i_mmap_rwsem in struct address_space to avoid false sharing
between i_mmap and i_mmap_rwsem.
- Convert efs, qnx4, and coda to use the new mount api.
- Add a generic is_dot_dotdot() helper that's used by various
filesystems and the VFS code instead of open-coding it multiple
times.
- Recently we've added stable offsets which allows stable ordering
when iterating directories exported through NFS on e.g., tmpfs
filesystems. Originally an xarray was used for the offset map but
that caused slab fragmentation issues over time. This switches the
offset map to the maple tree which has a dense mode that handles
this scenario a lot better. Includes tests.
- Finally merge the case-insensitive improvement series Gabriel has
been working on for a long time. This cleanly propagates case
insensitive operations through ->s_d_op which in turn allows us to
remove the quite ugly generic_set_encrypted_ci_d_ops() operations.
It also improves performance by trying a case-sensitive comparison
first and then fallback to case-insensitive lookup if that fails.
This also fixes a bug where overlayfs would be able to be mounted
over a case insensitive directory which would lead to all sort of
odd behaviors.
Cleanups:
- Make file_dentry() a simple accessor now that ->d_real() is
simplified because of the backing file work we did the last two
cycles.
- Use the dedicated file_mnt_idmap helper in ntfs3.
- Use smp_load_acquire/store_release() in the i_size_read/write
helpers and thus remove the hack to handle i_size reads in the
filemap code.
- The SLAB_MEM_SPREAD is a nop now. Remove it from various places in
fs/
- It's no longer necessary to perform a second built-in initramfs
unpack call because we retain the contents of the previous
extraction. Remove it.
- Now that we have removed various allocators kfree_rcu() always
works with kmem caches and kmalloc(). So simplify various places
that only use an rcu callback in order to handle the kmem cache
case.
- Convert the pipe code to use a lockdep comparison function instead
of open-coding the nesting making lockdep validation easier.
- Move code into fs-writeback.c that was located in a header but can
be made static as it's only used in that one file.
- Rewrite the alignment checking iterators for iovec and bvec to be
easier to read, and also significantly more compact in terms of
generated code. This saves 270 bytes of text on x86-64 (with
clang-18) and 224 bytes on arm64 (with gcc-13). In profiles it also
saves a bit of time for the same workload.
- Switch various places to use KMEM_CACHE instead of
kmem_cache_create().
- Use inode_set_ctime_to_ts() in inode_set_ctime_current()
- Use kzalloc() in name_to_handle_at() to avoid kernel infoleak.
- Various smaller cleanups for eventfds.
Fixes:
- Fix various comments and typos, and unneeded initializations.
- Fix stack allocation hack for clang in the select code.
- Improve dump_mapping() debug code on a best-effort basis.
- Fix build errors in various selftests.
- Avoid wrap-around instrumentation in various places.
- Don't allow user namespaces without an idmapping to be used for
idmapped mounts.
- Fix sysv sb_read() call.
- Fix fallback implementation of the get_name() export operation"
* tag 'vfs-6.9.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (70 commits)
hugetlbfs: support idmapped mounts
qnx4: convert qnx4 to use the new mount api
fs: use inode_set_ctime_to_ts to set inode ctime to current time
libfs: Drop generic_set_encrypted_ci_d_ops
ubifs: Configure dentry operations at dentry-creation time
f2fs: Configure dentry operations at dentry-creation time
ext4: Configure dentry operations at dentry-creation time
libfs: Add helper to choose dentry operations at mount-time
libfs: Merge encrypted_ci_dentry_ops and ci_dentry_ops
fscrypt: Drop d_revalidate once the key is added
fscrypt: Drop d_revalidate for valid dentries during lookup
fscrypt: Factor out a helper to configure the lookup dentry
ovl: Always reject mounting over case-insensitive directories
libfs: Attempt exact-match comparison first during casefolded lookup
efs: remove SLAB_MEM_SPREAD flag usage
jfs: remove SLAB_MEM_SPREAD flag usage
minix: remove SLAB_MEM_SPREAD flag usage
openpromfs: remove SLAB_MEM_SPREAD flag usage
proc: remove SLAB_MEM_SPREAD flag usage
qnx6: remove SLAB_MEM_SPREAD flag usage
...
This reverts commit 5785160732.
Unfortunately, while we only call that thing once, the callback
*can* be called more than once for the same dentry - all it
takes is rename_lock being touched while we are in d_walk().
For now let's revert it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
change of locking rules for __dentry_kill(), regularized refcounting
rules in that area, assorted cleanups and removal of weird corner
cases (e.g. now ->d_iput() on child is always called before the parent
might hit __dentry_kill(), etc.)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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Merge tag 'pull-dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull dcache updates from Al Viro:
"Change of locking rules for __dentry_kill(), regularized refcounting
rules in that area, assorted cleanups and removal of weird corner
cases (e.g. now ->d_iput() on child is always called before the parent
might hit __dentry_kill(), etc)"
* tag 'pull-dcache' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (40 commits)
dcache: remove unnecessary NULL check in dget_dlock()
kill DCACHE_MAY_FREE
__d_unalias() doesn't use inode argument
d_alloc_parallel(): in-lookup hash insertion doesn't need an RCU variant
get rid of DCACHE_GENOCIDE
d_genocide(): move the extern into fs/internal.h
simple_fill_super(): don't bother with d_genocide() on failure
nsfs: use d_make_root()
d_alloc_pseudo(): move setting ->d_op there from the (sole) caller
kill d_instantate_anon(), fold __d_instantiate_anon() into remaining caller
retain_dentry(): introduce a trimmed-down lockless variant
__dentry_kill(): new locking scheme
d_prune_aliases(): use a shrink list
switch select_collect{,2}() to use of to_shrink_list()
to_shrink_list(): call only if refcount is 0
fold dentry_kill() into dput()
don't try to cut corners in shrink_lock_dentry()
fold the call of retain_dentry() into fast_dput()
Call retain_dentry() with refcount 0
dentry_kill(): don't bother with retain_dentry() on slow path
...
To help make the move of sysctls out of kernel/sysctl.c not incur a size
penalty sysctl has been changed to allow us to not require the sentinel, the
final empty element on the sysctl array. Joel Granados has been doing all this
work. On the v6.6 kernel we got the major infrastructure changes required to
support this. For v6.7 we had all arch/ and drivers/ modified to remove
the sentinel. For v6.8-rc1 we get a few more updates for fs/ directory only.
The kernel/ directory is left but we'll save that for v6.9-rc1 as those patches
are still being reviewed. After that we then can expect also the removal of the
no longer needed check for procname == NULL.
Let us recap the purpose of this work:
- this helps reduce the overall build time size of the kernel and run time
memory consumed by the kernel by about ~64 bytes per array
- the extra 64-byte penalty is no longer inncurred now when we move sysctls
out from kernel/sysctl.c to their own files
Thomas Weißschuh also sent a few cleanups, for v6.9-rc1 we expect to see further
work by Thomas Weißschuh with the constificatin of the struct ctl_table.
Due to Joel Granados's work, and to help bring in new blood, I have suggested
for him to become a maintainer and he's accepted. So for v6.9-rc1 I look forward
to seeing him sent you a pull request for further sysctl changes. This also
removes Iurii Zaikin as a maintainer as he has moved on to other projects and
has had no time to help at all.
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Merge tag 'sysctl-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux
Pull sysctl updates from Luis Chamberlain:
"To help make the move of sysctls out of kernel/sysctl.c not incur a
size penalty sysctl has been changed to allow us to not require the
sentinel, the final empty element on the sysctl array. Joel Granados
has been doing all this work.
In the v6.6 kernel we got the major infrastructure changes required to
support this. For v6.7 we had all arch/ and drivers/ modified to
remove the sentinel. For v6.8-rc1 we get a few more updates for fs/
directory only.
The kernel/ directory is left but we'll save that for v6.9-rc1 as
those patches are still being reviewed. After that we then can expect
also the removal of the no longer needed check for procname == NULL.
Let us recap the purpose of this work:
- this helps reduce the overall build time size of the kernel and run
time memory consumed by the kernel by about ~64 bytes per array
- the extra 64-byte penalty is no longer inncurred now when we move
sysctls out from kernel/sysctl.c to their own files
Thomas Weißschuh also sent a few cleanups, for v6.9-rc1 we expect to
see further work by Thomas Weißschuh with the constificatin of the
struct ctl_table.
Due to Joel Granados's work, and to help bring in new blood, I have
suggested for him to become a maintainer and he's accepted. So for
v6.9-rc1 I look forward to seeing him sent you a pull request for
further sysctl changes. This also removes Iurii Zaikin as a maintainer
as he has moved on to other projects and has had no time to help at
all"
* tag 'sysctl-6.8-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux:
sysctl: remove struct ctl_path
sysctl: delete unused define SYSCTL_PERM_EMPTY_DIR
coda: Remove the now superfluous sentinel elements from ctl_table array
sysctl: Remove the now superfluous sentinel elements from ctl_table array
fs: Remove the now superfluous sentinel elements from ctl_table array
cachefiles: Remove the now superfluous sentinel element from ctl_table array
sysclt: Clarify the results of selftest run
sysctl: Add a selftest for handling empty dirs
sysctl: Fix out of bounds access for empty sysctl registers
MAINTAINERS: Add Joel Granados as co-maintainer for proc sysctl
MAINTAINERS: remove Iurii Zaikin from proc sysctl
This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which
will reduce the overall build time size of the kernel and run time
memory bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)
Remove sentinel elements ctl_table struct. Special attention was placed in
making sure that an empty directory for fs/verity was created when
CONFIG_FS_VERITY_BUILTIN_SIGNATURES is not defined. In this case we use the
register sysctl call that expects a size.
Signed-off-by: Joel Granados <j.granados@samsung.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Patch series "workload-specific and memory pressure-driven zswap
writeback", v8.
There are currently several issues with zswap writeback:
1. There is only a single global LRU for zswap, making it impossible to
perform worload-specific shrinking - an memcg under memory pressure
cannot determine which pages in the pool it owns, and often ends up
writing pages from other memcgs. This issue has been previously
observed in practice and mitigated by simply disabling
memcg-initiated shrinking:
https://lore.kernel.org/all/20230530232435.3097106-1-nphamcs@gmail.com/T/#u
But this solution leaves a lot to be desired, as we still do not
have an avenue for an memcg to free up its own memory locked up in
the zswap pool.
2. We only shrink the zswap pool when the user-defined limit is hit.
This means that if we set the limit too high, cold data that are
unlikely to be used again will reside in the pool, wasting precious
memory. It is hard to predict how much zswap space will be needed
ahead of time, as this depends on the workload (specifically, on
factors such as memory access patterns and compressibility of the
memory pages).
This patch series solves these issues by separating the global zswap LRU
into per-memcg and per-NUMA LRUs, and performs workload-specific (i.e
memcg- and NUMA-aware) zswap writeback under memory pressure. The new
shrinker does not have any parameter that must be tuned by the user, and
can be opted in or out on a per-memcg basis.
As a proof of concept, we ran the following synthetic benchmark: build the
linux kernel in a memory-limited cgroup, and allocate some cold data in
tmpfs to see if the shrinker could write them out and improved the overall
performance. Depending on the amount of cold data generated, we observe
from 14% to 35% reduction in kernel CPU time used in the kernel builds.
This patch (of 6):
The interface of list_lru is based on the assumption that the list node
and the data it represents belong to the same allocated on the correct
node/memcg. While this assumption is valid for existing slab objects LRU
such as dentries and inodes, it is undocumented, and rather inflexible for
certain potential list_lru users (such as the upcoming zswap shrinker and
the THP shrinker). It has caused us a lot of issues during our
development.
This patch changes list_lru interface so that the caller must explicitly
specify numa node and memcg when adding and removing objects. The old
list_lru_add() and list_lru_del() are renamed to list_lru_add_obj() and
list_lru_del_obj(), respectively.
It also extends the list_lru API with a new function, list_lru_putback,
which undoes a previous list_lru_isolate call. Unlike list_lru_add, it
does not increment the LRU node count (as list_lru_isolate does not
decrement the node count). list_lru_putback also allows for explicit
memcg and NUMA node selection.
Link: https://lkml.kernel.org/r/20231130194023.4102148-1-nphamcs@gmail.com
Link: https://lkml.kernel.org/r/20231130194023.4102148-2-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
dget_dlock() requires dentry->d_lock to be held when called, yet
contains a NULL check for dentry.
An audit of all calls to dget_dlock() shows that it is never called
with a NULL pointer (as spin_lock()/spin_unlock() would crash in these
cases):
$ git grep -W '\<dget_dlock\>'
arch/powerpc/platforms/cell/spufs/inode.c- spin_lock(&dentry->d_lock);
arch/powerpc/platforms/cell/spufs/inode.c- if (simple_positive(dentry)) {
arch/powerpc/platforms/cell/spufs/inode.c: dget_dlock(dentry);
fs/autofs/expire.c- spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
fs/autofs/expire.c- if (simple_positive(child)) {
fs/autofs/expire.c: dget_dlock(child);
fs/autofs/root.c: dget_dlock(active);
fs/autofs/root.c- spin_unlock(&active->d_lock);
fs/autofs/root.c: dget_dlock(expiring);
fs/autofs/root.c- spin_unlock(&expiring->d_lock);
fs/ceph/dir.c- if (!spin_trylock(&dentry->d_lock))
fs/ceph/dir.c- continue;
[...]
fs/ceph/dir.c: dget_dlock(dentry);
fs/ceph/mds_client.c- spin_lock(&alias->d_lock);
[...]
fs/ceph/mds_client.c: dn = dget_dlock(alias);
fs/configfs/inode.c- spin_lock(&dentry->d_lock);
fs/configfs/inode.c- if (simple_positive(dentry)) {
fs/configfs/inode.c: dget_dlock(dentry);
fs/libfs.c: found = dget_dlock(d);
fs/libfs.c- spin_unlock(&d->d_lock);
fs/libfs.c: found = dget_dlock(child);
fs/libfs.c- spin_unlock(&child->d_lock);
fs/libfs.c: child = dget_dlock(d);
fs/libfs.c- spin_unlock(&d->d_lock);
fs/ocfs2/dcache.c: dget_dlock(dentry);
fs/ocfs2/dcache.c- spin_unlock(&dentry->d_lock);
include/linux/dcache.h:static inline struct dentry *dget_dlock(struct dentry *dentry)
After taking out the NULL check, dget_dlock() becomes almost identical
to __dget_dlock(); the only difference is that dget_dlock() returns the
dentry that was passed in. These are static inline helpers, so we can
rely on the compiler to discard unused return values. We can therefore
also remove __dget_dlock() and replace calls to it by dget_dlock().
Also fix up and improve the kerneldoc comments while we're at it.
Al Viro pointed out that we can also clean up some of the callers to
make use of the returned value and provided a bit more info for the
kerneldoc.
While preparing v2 I also noticed that the tabs used in the kerneldoc
comments were causing the kerneldoc to get parsed incorrectly so I also
fixed this up (including for d_unhashed, which is otherwise unrelated).
Testing: x86 defconfig build + boot; make htmldocs for the kerneldoc
warning. objdump shows there are code generation changes.
Link: https://lore.kernel.org/all/20231022164520.915013-1-vegard.nossum@oracle.com/
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
With the new ordering in __dentry_kill() it has become redundant -
it's set if and only if both DCACHE_DENTRY_KILLED and DCACHE_SHRINK_LIST
are set.
We set it in __dentry_kill(), after having set DCACHE_DENTRY_KILLED
with the only condition being that DCACHE_SHRINK_LIST is there;
all of that is done without dropping ->d_lock and the only place
that checks that flag (shrink_dentry_list()) does so under ->d_lock,
after having found the victim on its shrink list. Since DCACHE_SHRINK_LIST
is set only when placing dentry into shrink list and removed only by
shrink_dentry_list() itself, a check for DCACHE_DENTRY_KILLED in
there would be equivalent to check for DCACHE_MAY_FREE.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We only search in the damn thing under hlist_bl_lock(); RCU variant
of insertion was, IIRC, pretty much cargo-culted - mea culpa...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
now that the only user of d_instantiate_anon() is gone...
[braino fix folded - kudos to Dan Carpenter]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
fast_dput() contains a small piece of code, preceded by scary
comments about 5 times longer than it. What is actually done there is
a trimmed-down subset of retain_dentry() - in some situations we can
tell that retain_dentry() would have returned true without ever needing
->d_lock and that's what that code checks. If these checks come true
fast_dput() can declare that we are done, without bothering with ->d_lock;
otherwise it has to take the lock and do full variant of retain_dentry()
checks.
Trimmed-down variant of the checks is hard to follow and
it's asking for trouble - if we ever decide to change the rules in
retain_dentry(), we'll have to remember to update that code. It turns
out that an equivalent variant of these checks more obviously parallel
to retain_dentry() is not just possible, but easy to unify with
retain_dentry() itself, passing it a new boolean argument ('locked')
to distinguish between the full semantics and trimmed down one.
Note that in lockless case true is returned only when locked
variant would have returned true without ever needing the lock; false
means "punt to the locking path and recheck there".
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Currently we enter __dentry_kill() with parent (along with the victim
dentry and victim's inode) held locked. Then we
mark dentry refcount as dead
call ->d_prune()
remove dentry from hash
remove it from the parent's list of children
unlock the parent, don't need it from that point on
detach dentry from inode, unlock dentry and drop the inode
(via ->d_iput())
call ->d_release()
regain the lock on dentry
check if it's on a shrink list (in which case freeing its empty husk
has to be left to shrink_dentry_list()) or not (in which case we can free it
ourselves). In the former case, mark it as an empty husk, so that
shrink_dentry_list() would know it can free the sucker.
drop the lock on dentry
... and usually the caller proceeds to drop a reference on the parent,
possibly retaking the lock on it.
That is painful for a bunch of reasons, starting with the need to take locks
out of order, but not limited to that - the parent of positive dentry can
change if we drop its ->d_lock, so getting these locks has to be done with
care. Moreover, as soon as dentry is out of the parent's list of children,
shrink_dcache_for_umount() won't see it anymore, making it appear as if
the parent is inexplicably busy. We do work around that by having
shrink_dentry_list() decrement the parent's refcount first and put it on
shrink list to be evicted once we are done with __dentry_kill() of child,
but that may in some cases lead to ->d_iput() on child called after the
parent got killed. That doesn't happen in cases where in-tree ->d_iput()
instances might want to look at the parent, but that's brittle as hell.
Solution: do removal from the parent's list of children in the very
end of __dentry_kill(). As the result, the callers do not need to
lock the parent and by the time we really need the parent locked,
dentry is negative and is guaranteed not to be moved around.
It does mean that ->d_prune() will be called with parent not locked.
It also means that we might see dentries in process of being torn
down while going through the parent's list of children; those dentries
will be unhashed, negative and with refcount marked dead. In practice,
that's enough for in-tree code that looks through the list of children
to do the right thing as-is. Out-of-tree code might need to be adjusted.
Calling conventions: __dentry_kill(dentry) is called with dentry->d_lock
held, along with ->i_lock of its inode (if any). It either returns
the parent (locked, with refcount decremented to 0) or NULL (if there'd
been no parent or if refcount decrement for parent hadn't reached 0).
lock_for_kill() is adjusted for new requirements - it doesn't touch
the parent's ->d_lock at all.
Callers adjusted. Note that for dput() we don't need to bother with
fast_dput() for the parent - we just need to check retain_dentry()
for it, since its ->d_lock is still held since the moment when
__dentry_kill() had taken it to remove the victim from the list of
children.
The kludge with early decrement of parent's refcount in
shrink_dentry_list() is no longer needed - shrink_dcache_for_umount()
sees the half-killed dentries in the list of children for as long
as they are pinning the parent. They are easily recognized and
accounted for by select_collect(), so we know we are not done yet.
As the result, we always have the expected ordering for ->d_iput()/->d_release()
vs. __dentry_kill() of the parent, no exceptions. Moreover, the current
rules for shrink lists (one must make sure that shrink_dcache_for_umount()
won't happen while any dentries from the superblock in question are on
any shrink lists) are gone - shrink_dcache_for_umount() will do the
right thing in all cases, taking such dentries out. Their empty
husks (memory occupied by struct dentry itself + its external name,
if any) will remain on the shrink lists, but they are no obstacles
to filesystem shutdown. And such husks will get freed as soon as
shrink_dentry_list() of the list they are on gets to them.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Instead of dropping aliases one by one, restarting, etc., just
collect them into a shrink list and kill them off in one pass.
We don't really need the restarts - one alias can't pin another
(directory has only one alias, and couldn't be its own ancestor
anyway), so collecting everything that is not busy and taking it
out would take care of everything evictable that had been there
as we entered the function. And new aliases added while we'd
been dropping old ones could just as easily have appeared right
as we return to caller...
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The only thing it does if refcount is not zero is d_lru_del(); no
point, IMO, seeing that plain dput() does nothing of that sort...
Note that 2 of 3 current callers are guaranteed that refcount is 0.
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
That is to say, do *not* treat the ->d_inode or ->d_parent changes
as "it's hard, return false; somebody must have grabbed it, so
even if has zero refcount, we don't need to bother killing it -
final dput() from whoever grabbed it would've done everything".
First of all, that is not guaranteed. It might have been dropped
by shrink_kill() handling of victim's parent, which would've found
it already on a shrink list (ours) and decided that they don't need
to put it on their shrink list.
What's more, dentry_kill() is doing pretty much the same thing,
cutting its own set of corners (it assumes that dentry can't
go from positive to negative, so its inode can change but only once
and only in one direction).
Doing that right allows to get rid of that not-quite-duplication
and removes the only reason for re-incrementing refcount before
the call of dentry_kill().
Replacement is called lock_for_kill(); called under rcu_read_lock
and with ->d_lock held. If it returns false, dentry has non-zero
refcount and the same locks are held. If it returns true,
dentry has zero refcount and all locks required by __dentry_kill()
are taken.
Part of __lock_parent() had been lifted into lock_parent() to
allow its reuse. Now it's called with rcu_read_lock already
held and dentry already unlocked.
Note that this is not the final change - locking requirements for
__dentry_kill() are going to change later in the series and the
set of locks taken by lock_for_kill() will be adjusted. Both
lock_parent() and __lock_parent() will be gone once that happens.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Calls of retain_dentry() happen immediately after getting false
from fast_dput() and getting true from retain_dentry() is
treated the same way as non-zero refcount would be treated by
fast_dput() - unlock dentry and bugger off.
Doing that in fast_dput() itself is simpler.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Instead of bumping it from 0 to 1, calling retain_dentry(), then
decrementing it back to 0 (with ->d_lock held all the way through),
just leave refcount at 0 through all of that.
It will have a visible effect for ->d_delete() - now it can be
called with refcount 0 instead of 1 and it can no longer play
silly buggers with dropping/regaining ->d_lock. Not that any
in-tree instances tried to (it's pretty hard to get right).
Any out-of-tree ones will have to adjust (assuming they need any
changes).
Note that we do not need to extend rcu-critical area here - we have
verified that refcount is non-negative after having grabbed ->d_lock,
so nobody will be able to free dentry until they get into __dentry_kill(),
which won't happen until they manage to grab ->d_lock.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We have already checked it and dentry used to look not worthy
of keeping. The only hard obstacle to evicting dentry is
non-zero refcount; everything else is advisory - e.g. memory
pressure could evict any dentry found with refcount zero.
On the slow path in dentry_kill() we had dropped and regained
->d_lock; we must recheck the refcount, but everything else
is not worth bothering with.
Note that filesystem can not count upon ->d_delete() being
called for dentry - not even once. Again, memory pressure
(as well as d_prune_aliases(), or attempted rmdir() of ancestor,
or...) will not call ->d_delete() at all.
So from the correctness point of view we are fine doing the
check only once. And it makes things simpler down the road.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Currently we call it with refcount equal to 1 when called from
dentry_kill(); all other callers have it equal to 0.
Make it always be called with zero refcount; on this step we
just decrement it before the calls in dentry_kill(). That is
safe, since all places that care about the value of refcount
either do that under ->d_lock or hold a reference to dentry
in question. Either is sufficient to prevent observing a
dentry immediately prior to __dentry_kill() getting called
from dentry_kill().
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
retain_dentry() used to decrement refcount if and only if it returned
true. Lift those decrements into the callers.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... and rename it to to_shrink_list(), seeing that it no longer
does dropping any references
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
By now there is only one place in entire fast_dput() where we return
false; that happens after refcount had been decremented and found (under
->d_lock) to be zero. In that case, just prior to returning false to
caller, fast_dput() forcibly changes the refcount from 0 to 1.
Lift that resetting refcount to 1 into the callers; later in the series
it will be massaged out of existence.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
If refcount is less than 1, we should just warn, unlock dentry and
return true, so that the caller doesn't try to do anything else.
Taking care of that leaves the rest of "lockref_put_return() has
failed" case equivalent to "decrement refcount and rejoin the
normal slow path after the point where we grab ->d_lock".
NOTE: lockref_put_return() is strictly a fastpath thing - unlike
the rest of lockref primitives, it does not contain a fallback.
Caller (and it looks like fast_dput() is the only legitimate one
in the entire kernel) has to do that itself. Reasons for
lockref_put_return() failures:
* ->d_lock held by somebody
* refcount <= 0
* ... or an architecture not supporting lockref use of
cmpxchg - sparc, anything non-SMP, config with spinlock debugging...
We could add a fallback, but it would be a clumsy API - we'd have
to distinguish between:
(1) refcount > 1 - decremented, lock not held on return
(2) refcount < 1 - left alone, probably no sense to hold the lock
(3) refcount is 1, no cmphxcg - decremented, lock held on return
(4) refcount is 1, cmphxcg supported - decremented, lock *NOT* held
on return.
We want to return with no lock held in case (4); that's the whole point of that
thing. We very much do not want to have the fallback in case (3) return without
a lock, since the caller might have to retake it in that case.
So it wouldn't be more convenient than doing the fallback in the caller and
it would be very easy to screw up, especially since the test coverage would
suck - no way to test (3) and (4) on the same kernel build.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
->d_delete() is a way for filesystem to tell that dentry is not worth
keeping cached. It is not guaranteed to be called every time a dentry
has refcount drop down to zero; it is not guaranteed to be called before
dentry gets evicted. In other words, it is not suitable for any kind
of keeping track of dentry state.
None of the in-tree filesystems attempt to use it that way, fortunately.
So the contortions done by fast_dput() (as well as dentry_kill()) are
not warranted. fast_dput() certainly should treat having ->d_delete()
instance as "can't assume we'll be keeping it", but that's not different
from the way we treat e.g. DCACHE_DONTCACHE (which is rather similar
to making ->d_delete() returns true when called).
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... we won't see DCACHE_MAY_FREE on anything that is *not* dead
and checking d_flags is just as cheap as checking refcount.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
new helper unifying identical bits of shrink_dentry_list() and
shring_dcache_for_umount()
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Saves a pointer per struct dentry and actually makes the things less
clumsy. Cleaned the d_walk() and dcache_readdir() a bit by use
of hlist_for_... iterators.
A couple of new helpers - d_first_child() and d_next_sibling(),
to make the expressions less awful.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
there's little I can say which isn't in the individual changelogs.
The lengthier patch series are
- "kdump: use generic functions to simplify crashkernel reservation in
arch", from Baoquan He. This is mainly cleanups and consolidation of
the "crashkernel=" kernel parameter handling.
- After much discussion, David Laight's "minmax: Relax type checks in
min() and max()" is here. Hopefully reduces some typecasting and the
use of min_t() and max_t().
- A group of patches from Oleg Nesterov which clean up and slightly fix
our handling of reads from /proc/PID/task/... and which remove
task_struct.therad_group.
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Merge tag 'mm-nonmm-stable-2023-11-02-14-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Pull non-MM updates from Andrew Morton:
"As usual, lots of singleton and doubleton patches all over the tree
and there's little I can say which isn't in the individual changelogs.
The lengthier patch series are
- 'kdump: use generic functions to simplify crashkernel reservation
in arch', from Baoquan He. This is mainly cleanups and
consolidation of the 'crashkernel=' kernel parameter handling
- After much discussion, David Laight's 'minmax: Relax type checks in
min() and max()' is here. Hopefully reduces some typecasting and
the use of min_t() and max_t()
- A group of patches from Oleg Nesterov which clean up and slightly
fix our handling of reads from /proc/PID/task/... and which remove
task_struct.thread_group"
* tag 'mm-nonmm-stable-2023-11-02-14-08' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (64 commits)
scripts/gdb/vmalloc: disable on no-MMU
scripts/gdb: fix usage of MOD_TEXT not defined when CONFIG_MODULES=n
.mailmap: add address mapping for Tomeu Vizoso
mailmap: update email address for Claudiu Beznea
tools/testing/selftests/mm/run_vmtests.sh: lower the ptrace permissions
.mailmap: map Benjamin Poirier's address
scripts/gdb: add lx_current support for riscv
ocfs2: fix a spelling typo in comment
proc: test ProtectionKey in proc-empty-vm test
proc: fix proc-empty-vm test with vsyscall
fs/proc/base.c: remove unneeded semicolon
do_io_accounting: use sig->stats_lock
do_io_accounting: use __for_each_thread()
ocfs2: replace BUG_ON() at ocfs2_num_free_extents() with ocfs2_error()
ocfs2: fix a typo in a comment
scripts/show_delta: add __main__ judgement before main code
treewide: mark stuff as __ro_after_init
fs: ocfs2: check status values
proc: test /proc/${pid}/statm
compiler.h: move __is_constexpr() to compiler.h
...
__read_mostly predates __ro_after_init. Many variables which are marked
__read_mostly should have been __ro_after_init from day 1.
Also, mark some stuff as "const" and "__init" while I'm at it.
[akpm@linux-foundation.org: revert sysctl_nr_open_min, sysctl_nr_open_max changes due to arm warning]
[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/4f6bb9c0-abba-4ee4-a7aa-89265e886817@p183
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
New helper for bcachefs - bcachefs doesn't want the
inode_dec_link_count() call that d_tmpfile does, it handles i_nlink on
its own atomically with other btree updates
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Use WARN instead of printk + WARN_ON as reported from coccinelle:
./fs/dcache.c:1667:1-7: SUGGESTION: printk + WARN_ON can be just WARN
Signed-off-by: Anh Tuan Phan <tuananhlfc@gmail.com>
Message-Id: <20230817163142.117706-1-tuananhlfc@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
d_genocide is only used by built-in code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Message-Id: <20230808161704.1099680-1-hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'pull-tmpfile' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs tmpfile updates from Al Viro:
"Miklos' ->tmpfile() signature change; pass an unopened struct file to
it, let it open the damn thing. Allows to add tmpfile support to FUSE"
* tag 'pull-tmpfile' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
fuse: implement ->tmpfile()
vfs: open inside ->tmpfile()
vfs: move open right after ->tmpfile()
vfs: make vfs_tmpfile() static
ovl: use vfs_tmpfile_open() helper
cachefiles: use vfs_tmpfile_open() helper
cachefiles: only pass inode to *mark_inode_inuse() helpers
cachefiles: tmpfile error handling cleanup
hugetlbfs: cleanup mknod and tmpfile
vfs: add vfs_tmpfile_open() helper
This is in preparation for adding tmpfile support to fuse, which requires
that the tmpfile creation and opening are done as a single operation.
Replace the 'struct dentry *' argument of i_op->tmpfile with
'struct file *'.
Call finish_open_simple() as the last thing in ->tmpfile() instances (may
be omitted in the error case).
Change d_tmpfile() argument to 'struct file *' as well to make callers more
readable.
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Replace the open coded CONFIG_PREEMPT_RT conditional
preempt_disable/enable() with the new helper.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Link: https://lore.kernel.org/r/20220825164131.402717-3-bigeasy@linutronix.de
__d_lookup_rcu() is one of the hottest functions in the kernel on
certain loads, and it is complicated by filesystems that might want to
have their own name compare function.
We can improve code generation by moving the test of DCACHE_OP_COMPARE
outside the loop, which makes the loop itself much simpler, at the cost
of some code duplication. But both cases end up being simpler, and the
"native" direct case-sensitive compare particularly so.
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Luis and others, almost exclusively in the filesystem. Several patches
touch files outside of our normal purview to set the stage for bringing
in Jeff's long awaited ceph+fscrypt series in the near future. All of
them have appropriate acks and sat in linux-next for a while.
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Merge tag 'ceph-for-5.20-rc1' of https://github.com/ceph/ceph-client
Pull ceph updates from Ilya Dryomov:
"We have a good pile of various fixes and cleanups from Xiubo, Jeff,
Luis and others, almost exclusively in the filesystem.
Several patches touch files outside of our normal purview to set the
stage for bringing in Jeff's long awaited ceph+fscrypt series in the
near future. All of them have appropriate acks and sat in linux-next
for a while"
* tag 'ceph-for-5.20-rc1' of https://github.com/ceph/ceph-client: (27 commits)
libceph: clean up ceph_osdc_start_request prototype
libceph: fix ceph_pagelist_reserve() comment typo
ceph: remove useless check for the folio
ceph: don't truncate file in atomic_open
ceph: make f_bsize always equal to f_frsize
ceph: flush the dirty caps immediatelly when quota is approaching
libceph: print fsid and epoch with osd id
libceph: check pointer before assigned to "c->rules[]"
ceph: don't get the inline data for new creating files
ceph: update the auth cap when the async create req is forwarded
ceph: make change_auth_cap_ses a global symbol
ceph: fix incorrect old_size length in ceph_mds_request_args
ceph: switch back to testing for NULL folio->private in ceph_dirty_folio
ceph: call netfs_subreq_terminated with was_async == false
ceph: convert to generic_file_llseek
ceph: fix the incorrect comment for the ceph_mds_caps struct
ceph: don't leak snap_rwsem in handle_cap_grant
ceph: prevent a client from exceeding the MDS maximum xattr size
ceph: choose auth MDS for getxattr with the Xs caps
ceph: add session already open notify support
...
Compare dentry name with case-exact name, return true if names
are same, or false.
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
__d_add() and __d_move() wake up waiters on dentry::d_wait from within
the i_seq_dir write held region. This violates the PREEMPT_RT
constraints as the wake up acquires wait_queue_head::lock which is a
"sleeping" spinlock on RT.
There is no requirement to do so. __d_lookup_unhash() has cleared
DCACHE_PAR_LOOKUP and dentry::d_wait and returned the now unreachable wait
queue head pointer to the caller, so the actual wake up can be postponed
until the i_dir_seq write side critical section is left. The only
requirement is that dentry::lock is held across the whole sequence
including the wake up. The previous commit includes an analysis why this
is considered safe.
Move the wake up past end_dir_add() which leaves the i_dir_seq write side
critical section and enables preemption.
For non RT kernels there is no difference because preemption is still
disabled due to dentry::lock being held, but it shortens the time between
wake up and unlocking dentry::lock, which reduces the contention for the
woken up waiter.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
