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73 Commits
Author | SHA1 | Message | Date | |
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David Howells
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285e728b0a |
FS-Cache: Don't delete pending pages from the page-store tracking tree
Don't delete pending pages from the page-store tracking tree, but rather send them for another write as they've presumably been updated. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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1bccf513ac |
FS-Cache: Fix lock misorder in fscache_write_op()
FS-Cache has two structs internally for keeping track of the internal state of a cached file: the fscache_cookie struct, which represents the netfs's state, and fscache_object struct, which represents the cache's state. Each has a pointer that points to the other (when both are in existence), and each has a spinlock for pointer maintenance. Since netfs operations approach these structures from the cookie side, they get the cookie lock first, then the object lock. Cache operations, on the other hand, approach from the object side, and get the object lock first. It is not then permitted for a cache operation to get the cookie lock whilst it is holding the object lock lest deadlock occur; instead, it must do one of two things: (1) increment the cookie usage counter, drop the object lock and then get both locks in order, or (2) simply hold the object lock as certain parts of the cookie may not be altered whilst the object lock is held. It is also not permitted to follow either pointer without holding the lock at the end you start with. To break the pointers between the cookie and the object, both locks must be held. fscache_write_op(), however, violates the locking rules: It attempts to get the cookie lock without (a) checking that the cookie pointer is a valid pointer, and (b) holding the object lock to protect the cookie pointer whilst it follows it. This is so that it can access the pending page store tree without interference from __fscache_write_page(). This is fixed by splitting the cookie lock, such that the page store tracking tree is protected by its own lock, and checking that the cookie pointer is non-NULL before we attempt to follow it whilst holding the object lock. The new lock is subordinate to both the cookie lock and the object lock, and so should be taken after those. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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6897e3df8f |
FS-Cache: The object-available state can't rely on the cookie to be available
The object-available state in the object processing state machine (as processed by fscache_object_available()) can't rely on the cookie to be available because the FSCACHE_COOKIE_CREATING bit may have been cleared by fscache_obtained_object() prior to the object being put into the FSCACHE_OBJECT_AVAILABLE state. Clearing the FSCACHE_COOKIE_CREATING bit on a cookie permits __fscache_relinquish_cookie() to proceed and detach the cookie from the object. To deal with this, we don't dereference object->cookie in fscache_object_available() if the object has already been detached. In addition, a couple of assertions are added into fscache_drop_object() to make sure the object is unbound from the cookie before it gets there. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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5753c44188 |
FS-Cache: Permit cache retrieval ops to be interrupted in the initial wait phase
Permit the operations to retrieve data from the cache or to allocate space in the cache for future writes to be interrupted whilst they're waiting for permission for the operation to proceed. Typically this wait occurs whilst the cache object is being looked up on disk in the background. If an interruption occurs, and the operation has not yet been given the go-ahead to run, the operation is dequeued and cancelled, and control returns to the read operation of the netfs routine with none of the requested pages having been read or in any way marked as known by the cache. This means that the initial wait is done interruptibly rather than uninterruptibly. In addition, extra stats values are made available to show the number of ops cancelled and the number of cache space allocations interrupted. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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b34df792b4 |
FS-Cache: Use radix tree preload correctly in tracking of pages to be stored
__fscache_write_page() attempts to load the radix tree preallocation pool for the CPU it is on before calling radix_tree_insert(), as the insertion must be done inside a pair of spinlocks. Use of the preallocation pool, however, is contingent on the radix tree being initialised without __GFP_WAIT specified. __fscache_acquire_cookie() was passing GFP_NOFS to INIT_RADIX_TREE() - but that includes __GFP_WAIT. The solution is to AND out __GFP_WAIT. Additionally, the banner comment to radix_tree_preload() is altered to make note of this prerequisite. Possibly there should be a WARN_ON() too. Without this fix, I have seen the following recursive deadlock caused by radix_tree_insert() attempting to allocate memory inside the spinlocked region, which resulted in FS-Cache being called back into to release memory - which required the spinlock already held. ============================================= [ INFO: possible recursive locking detected ] 2.6.32-rc6-cachefs #24 --------------------------------------------- nfsiod/7916 is trying to acquire lock: (&cookie->lock){+.+.-.}, at: [<ffffffffa0076872>] __fscache_uncache_page+0xdb/0x160 [fscache] but task is already holding lock: (&cookie->lock){+.+.-.}, at: [<ffffffffa0076acc>] __fscache_write_page+0x15c/0x3f3 [fscache] other info that might help us debug this: 5 locks held by nfsiod/7916: #0: (nfsiod){+.+.+.}, at: [<ffffffff81048290>] worker_thread+0x19a/0x2e2 #1: (&task->u.tk_work#2){+.+.+.}, at: [<ffffffff81048290>] worker_thread+0x19a/0x2e2 #2: (&cookie->lock){+.+.-.}, at: [<ffffffffa0076acc>] __fscache_write_page+0x15c/0x3f3 [fscache] #3: (&object->lock#2){+.+.-.}, at: [<ffffffffa0076b07>] __fscache_write_page+0x197/0x3f3 [fscache] #4: (&cookie->stores_lock){+.+...}, at: [<ffffffffa0076b0f>] __fscache_write_page+0x19f/0x3f3 [fscache] stack backtrace: Pid: 7916, comm: nfsiod Not tainted 2.6.32-rc6-cachefs #24 Call Trace: [<ffffffff8105ac7f>] __lock_acquire+0x1649/0x16e3 [<ffffffff81059ded>] ? __lock_acquire+0x7b7/0x16e3 [<ffffffff8100e27d>] ? dump_trace+0x248/0x257 [<ffffffff8105ad70>] lock_acquire+0x57/0x6d [<ffffffffa0076872>] ? __fscache_uncache_page+0xdb/0x160 [fscache] [<ffffffff8135467c>] _spin_lock+0x2c/0x3b [<ffffffffa0076872>] ? __fscache_uncache_page+0xdb/0x160 [fscache] [<ffffffffa0076872>] __fscache_uncache_page+0xdb/0x160 [fscache] [<ffffffffa0077eb7>] ? __fscache_check_page_write+0x0/0x71 [fscache] [<ffffffffa00b4755>] nfs_fscache_release_page+0x86/0xc4 [nfs] [<ffffffffa00907f0>] nfs_release_page+0x3c/0x41 [nfs] [<ffffffff81087ffb>] try_to_release_page+0x32/0x3b [<ffffffff81092c2b>] shrink_page_list+0x316/0x4ac [<ffffffff81058a9b>] ? mark_held_locks+0x52/0x70 [<ffffffff8135451b>] ? _spin_unlock_irq+0x2b/0x31 [<ffffffff81093153>] shrink_inactive_list+0x392/0x67c [<ffffffff81058a9b>] ? mark_held_locks+0x52/0x70 [<ffffffff810934ca>] shrink_list+0x8d/0x8f [<ffffffff81093744>] shrink_zone+0x278/0x33c [<ffffffff81052c70>] ? ktime_get_ts+0xad/0xba [<ffffffff8109453b>] try_to_free_pages+0x22e/0x392 [<ffffffff8109184c>] ? isolate_pages_global+0x0/0x212 [<ffffffff8108e16b>] __alloc_pages_nodemask+0x3dc/0x5cf [<ffffffff810ae24a>] cache_alloc_refill+0x34d/0x6c1 [<ffffffff811bcf74>] ? radix_tree_node_alloc+0x52/0x5c [<ffffffff810ae929>] kmem_cache_alloc+0xb2/0x118 [<ffffffff811bcf74>] radix_tree_node_alloc+0x52/0x5c [<ffffffff811bcfd5>] radix_tree_insert+0x57/0x19c [<ffffffffa0076b53>] __fscache_write_page+0x1e3/0x3f3 [fscache] [<ffffffffa00b4248>] __nfs_readpage_to_fscache+0x58/0x11e [nfs] [<ffffffffa009bb77>] nfs_readpage_release+0x34/0x9b [nfs] [<ffffffffa009c0d9>] nfs_readpage_release_full+0x32/0x4b [nfs] [<ffffffffa0006cff>] rpc_release_calldata+0x12/0x14 [sunrpc] [<ffffffffa0006e2d>] rpc_free_task+0x59/0x61 [sunrpc] [<ffffffffa0006f03>] rpc_async_release+0x10/0x12 [sunrpc] [<ffffffff810482e5>] worker_thread+0x1ef/0x2e2 [<ffffffff81048290>] ? worker_thread+0x19a/0x2e2 [<ffffffff81352433>] ? thread_return+0x3e/0x101 [<ffffffffa0006ef3>] ? rpc_async_release+0x0/0x12 [sunrpc] [<ffffffff8104bff5>] ? autoremove_wake_function+0x0/0x34 [<ffffffff81058d25>] ? trace_hardirqs_on+0xd/0xf [<ffffffff810480f6>] ? worker_thread+0x0/0x2e2 [<ffffffff8104bd21>] kthread+0x7a/0x82 [<ffffffff8100beda>] child_rip+0xa/0x20 [<ffffffff8100b87c>] ? restore_args+0x0/0x30 [<ffffffff8104c2b9>] ? add_wait_queue+0x15/0x44 [<ffffffff8104bca7>] ? kthread+0x0/0x82 [<ffffffff8100bed0>] ? child_rip+0x0/0x20 Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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7e311a207d |
FS-Cache: Clear netfs pointers in cookie after detaching object, not before
Clear the pointers from the fscache_cookie struct to netfs private data after clearing the pointer to the cookie from the fscache_object struct and releasing the object lock, rather than before. This allows the netfs private data pointers to be relied on simply by holding the object lock, rather than having to hold the cookie lock. This is makes things simpler as the cookie lock has to be taken before the object lock, but sometimes the object pointer is all that the code has. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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52bd75fdb1 |
FS-Cache: Add counters for entry/exit to/from cache operation functions
Count entries to and exits from cache operation table functions. Maintain these as a single counter that's added to or removed from as appropriate. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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4fbf4291aa |
FS-Cache: Allow the current state of all objects to be dumped
Allow the current state of all fscache objects to be dumped by doing: cat /proc/fs/fscache/objects By default, all objects and all fields will be shown. This can be restricted by adding a suitable key to one of the caller's keyrings (such as the session keyring): keyctl add user fscache:objlist "<restrictions>" @s The <restrictions> are: K Show hexdump of object key (don't show if not given) A Show hexdump of object aux data (don't show if not given) And paired restrictions: C Show objects that have a cookie c Show objects that don't have a cookie B Show objects that are busy b Show objects that aren't busy W Show objects that have pending writes w Show objects that don't have pending writes R Show objects that have outstanding reads r Show objects that don't have outstanding reads S Show objects that have slow work queued s Show objects that don't have slow work queued If neither side of a restriction pair is given, then both are implied. For example: keyctl add user fscache:objlist KB @s shows objects that are busy, and lists their object keys, but does not dump their auxiliary data. It also implies "CcWwRrSs", but as 'B' is given, 'b' is not implied. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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440f0affe2 |
FS-Cache: Annotate slow-work runqueue proc lines for FS-Cache work items
Annotate slow-work runqueue proc lines for FS-Cache work items. Objects include the object ID and the state. Operations include the object ID, the operation ID and the operation type and state. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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3d7a641e54 |
SLOW_WORK: Wait for outstanding work items belonging to a module to clear
Wait for outstanding slow work items belonging to a module to clear when unregistering that module as a user of the facility. This prevents the put_ref code of a work item from being taken away before it returns. Signed-off-by: David Howells <dhowells@redhat.com> |
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David Howells
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348ca1029e |
FS-Cache: Fixup renamed filenames in comments in internal.h
Fix up renamed filenames in comments in fs/fscache/internal.h. Originally, the files were all called fsc-xxx.c, but they got renamed to just xxx.c. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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David Howells
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b510882281 |
FS-Cache: Implement data I/O part of netfs API
Implement the data I/O part of the FS-Cache netfs API. The documentation and API header file were added in a previous patch. This patch implements the following functions for the netfs to call: (*) fscache_attr_changed(). Indicate that the object has changed its attributes. The only attribute currently recorded is the file size. Only pages within the set file size will be stored in the cache. This operation is submitted for asynchronous processing, and will return immediately. It will return -ENOMEM if an out of memory error is encountered, -ENOBUFS if the object is not actually cached, or 0 if the operation is successfully queued. (*) fscache_read_or_alloc_page(). (*) fscache_read_or_alloc_pages(). Request data be fetched from the disk, and allocate internal metadata to track the netfs pages and reserve disk space for unknown pages. These operations perform semi-asynchronous data reads. Upon returning they will indicate which pages they think can be retrieved from disk, and will have set in progress attempts to retrieve those pages. These will return, in order of preference, -ENOMEM on memory allocation error, -ERESTARTSYS if a signal interrupted proceedings, -ENODATA if one or more requested pages are not yet cached, -ENOBUFS if the object is not actually cached or if there isn't space for future pages to be cached on this object, or 0 if successful. In the case of the multipage function, the pages for which reads are set in progress will be removed from the list and the page count decreased appropriately. If any read operations should fail, the completion function will be given an error, and will also be passed contextual information to allow the netfs to fall back to querying the server for the absent pages. For each successful read, the page completion function will also be called. Any pages subsequently tracked by the cache will have PG_fscache set upon them on return. fscache_uncache_page() must be called for such pages. If supplied by the netfs, the mark_pages_cached() cookie op will be invoked for any pages now tracked. (*) fscache_alloc_page(). Allocate internal metadata to track a netfs page and reserve disk space. This will return -ENOMEM on memory allocation error, -ERESTARTSYS on signal, -ENOBUFS if the object isn't cached, or there isn't enough space in the cache, or 0 if successful. Any pages subsequently tracked by the cache will have PG_fscache set upon them on return. fscache_uncache_page() must be called for such pages. If supplied by the netfs, the mark_pages_cached() cookie op will be invoked for any pages now tracked. (*) fscache_write_page(). Request data be stored to disk. This may only be called on pages that have been read or alloc'd by the above three functions and have not yet been uncached. This will return -ENOMEM on memory allocation error, -ERESTARTSYS on signal, -ENOBUFS if the object isn't cached, or there isn't immediately enough space in the cache, or 0 if successful. On a successful return, this operation will have queued the page for asynchronous writing to the cache. The page will be returned with PG_fscache_write set until the write completes one way or another. The caller will not be notified if the write fails due to an I/O error. If that happens, the object will become available and all pending writes will be aborted. Note that the cache may batch up page writes, and so it may take a while to get around to writing them out. The caller must assume that until PG_fscache_write is cleared the page is use by the cache. Any changes made to the page may be reflected on disk. The page may even be under DMA. (*) fscache_uncache_page(). Indicate that the cache should stop tracking a page previously read or alloc'd from the cache. If the page was alloc'd only, but unwritten, it will not appear on disk. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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952efe7b78 |
FS-Cache: Add and document asynchronous operation handling
Add and document asynchronous operation handling for use by FS-Cache's data storage and retrieval routines. The following documentation is added to: Documentation/filesystems/caching/operations.txt ================================ ASYNCHRONOUS OPERATIONS HANDLING ================================ ======== OVERVIEW ======== FS-Cache has an asynchronous operations handling facility that it uses for its data storage and retrieval routines. Its operations are represented by fscache_operation structs, though these are usually embedded into some other structure. This facility is available to and expected to be be used by the cache backends, and FS-Cache will create operations and pass them off to the appropriate cache backend for completion. To make use of this facility, <linux/fscache-cache.h> should be #included. =============================== OPERATION RECORD INITIALISATION =============================== An operation is recorded in an fscache_operation struct: struct fscache_operation { union { struct work_struct fast_work; struct slow_work slow_work; }; unsigned long flags; fscache_operation_processor_t processor; ... }; Someone wanting to issue an operation should allocate something with this struct embedded in it. They should initialise it by calling: void fscache_operation_init(struct fscache_operation *op, fscache_operation_release_t release); with the operation to be initialised and the release function to use. The op->flags parameter should be set to indicate the CPU time provision and the exclusivity (see the Parameters section). The op->fast_work, op->slow_work and op->processor flags should be set as appropriate for the CPU time provision (see the Parameters section). FSCACHE_OP_WAITING may be set in op->flags prior to each submission of the operation and waited for afterwards. ========== PARAMETERS ========== There are a number of parameters that can be set in the operation record's flag parameter. There are three options for the provision of CPU time in these operations: (1) The operation may be done synchronously (FSCACHE_OP_MYTHREAD). A thread may decide it wants to handle an operation itself without deferring it to another thread. This is, for example, used in read operations for calling readpages() on the backing filesystem in CacheFiles. Although readpages() does an asynchronous data fetch, the determination of whether pages exist is done synchronously - and the netfs does not proceed until this has been determined. If this option is to be used, FSCACHE_OP_WAITING must be set in op->flags before submitting the operation, and the operating thread must wait for it to be cleared before proceeding: wait_on_bit(&op->flags, FSCACHE_OP_WAITING, fscache_wait_bit, TASK_UNINTERRUPTIBLE); (2) The operation may be fast asynchronous (FSCACHE_OP_FAST), in which case it will be given to keventd to process. Such an operation is not permitted to sleep on I/O. This is, for example, used by CacheFiles to copy data from a backing fs page to a netfs page after the backing fs has read the page in. If this option is used, op->fast_work and op->processor must be initialised before submitting the operation: INIT_WORK(&op->fast_work, do_some_work); (3) The operation may be slow asynchronous (FSCACHE_OP_SLOW), in which case it will be given to the slow work facility to process. Such an operation is permitted to sleep on I/O. This is, for example, used by FS-Cache to handle background writes of pages that have just been fetched from a remote server. If this option is used, op->slow_work and op->processor must be initialised before submitting the operation: fscache_operation_init_slow(op, processor) Furthermore, operations may be one of two types: (1) Exclusive (FSCACHE_OP_EXCLUSIVE). Operations of this type may not run in conjunction with any other operation on the object being operated upon. An example of this is the attribute change operation, in which the file being written to may need truncation. (2) Shareable. Operations of this type may be running simultaneously. It's up to the operation implementation to prevent interference between other operations running at the same time. ========= PROCEDURE ========= Operations are used through the following procedure: (1) The submitting thread must allocate the operation and initialise it itself. Normally this would be part of a more specific structure with the generic op embedded within. (2) The submitting thread must then submit the operation for processing using one of the following two functions: int fscache_submit_op(struct fscache_object *object, struct fscache_operation *op); int fscache_submit_exclusive_op(struct fscache_object *object, struct fscache_operation *op); The first function should be used to submit non-exclusive ops and the second to submit exclusive ones. The caller must still set the FSCACHE_OP_EXCLUSIVE flag. If successful, both functions will assign the operation to the specified object and return 0. -ENOBUFS will be returned if the object specified is permanently unavailable. The operation manager will defer operations on an object that is still undergoing lookup or creation. The operation will also be deferred if an operation of conflicting exclusivity is in progress on the object. If the operation is asynchronous, the manager will retain a reference to it, so the caller should put their reference to it by passing it to: void fscache_put_operation(struct fscache_operation *op); (3) If the submitting thread wants to do the work itself, and has marked the operation with FSCACHE_OP_MYTHREAD, then it should monitor FSCACHE_OP_WAITING as described above and check the state of the object if necessary (the object might have died whilst the thread was waiting). When it has finished doing its processing, it should call fscache_put_operation() on it. (4) The operation holds an effective lock upon the object, preventing other exclusive ops conflicting until it is released. The operation can be enqueued for further immediate asynchronous processing by adjusting the CPU time provisioning option if necessary, eg: op->flags &= ~FSCACHE_OP_TYPE; op->flags |= ~FSCACHE_OP_FAST; and calling: void fscache_enqueue_operation(struct fscache_operation *op) This can be used to allow other things to have use of the worker thread pools. ===================== ASYNCHRONOUS CALLBACK ===================== When used in asynchronous mode, the worker thread pool will invoke the processor method with a pointer to the operation. This should then get at the container struct by using container_of(): static void fscache_write_op(struct fscache_operation *_op) { struct fscache_storage *op = container_of(_op, struct fscache_storage, op); ... } The caller holds a reference on the operation, and will invoke fscache_put_operation() when the processor function returns. The processor function is at liberty to call fscache_enqueue_operation() or to take extra references. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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ccc4fc3d11 |
FS-Cache: Implement the cookie management part of the netfs API
Implement the cookie management part of the FS-Cache netfs client API. The documentation and API header file were added in a previous patch. This patch implements the following three functions: (1) fscache_acquire_cookie(). Acquire a cookie to represent an object to the netfs. If the object in question is a non-index object, then that object and its parent indices will be created on disk at this point if they don't already exist. Index creation is deferred because an index may reside in multiple caches. (2) fscache_relinquish_cookie(). Retire or release a cookie previously acquired. At this point, the object on disk may be destroyed. (3) fscache_update_cookie(). Update the in-cache representation of a cookie. This is used to update the auxiliary data for coherency management purposes. With this patch it is possible to have a netfs instruct a cache backend to look up, validate and create metadata on disk and to destroy it again. The ability to actually store and retrieve data in the objects so created is added in later patches. Note that these functions will never return an error. _All_ errors are handled internally to FS-Cache. The worst that can happen is that fscache_acquire_cookie() may return a NULL pointer - which is considered a negative cookie pointer and can be passed back to any function that takes a cookie without harm. A negative cookie pointer merely suppresses caching at that level. The stub in linux/fscache.h will detect inline the negative cookie pointer and abort the operation as fast as possible. This means that the compiler doesn't have to set up for a call in that case. See the documentation in Documentation/filesystems/caching/netfs-api.txt for more information. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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36c9559022 |
FS-Cache: Object management state machine
Implement the cache object management state machine. The following documentation is added to illuminate the working of this state machine. It will also be added as: Documentation/filesystems/caching/object.txt ==================================================== IN-KERNEL CACHE OBJECT REPRESENTATION AND MANAGEMENT ==================================================== ============== REPRESENTATION ============== FS-Cache maintains an in-kernel representation of each object that a netfs is currently interested in. Such objects are represented by the fscache_cookie struct and are referred to as cookies. FS-Cache also maintains a separate in-kernel representation of the objects that a cache backend is currently actively caching. Such objects are represented by the fscache_object struct. The cache backends allocate these upon request, and are expected to embed them in their own representations. These are referred to as objects. There is a 1:N relationship between cookies and objects. A cookie may be represented by multiple objects - an index may exist in more than one cache - or even by no objects (it may not be cached). Furthermore, both cookies and objects are hierarchical. The two hierarchies correspond, but the cookies tree is a superset of the union of the object trees of multiple caches: NETFS INDEX TREE : CACHE 1 : CACHE 2 : : : +-----------+ : +----------->| IObject | : +-----------+ | : +-----------+ : | ICookie |-------+ : | : +-----------+ | : | : +-----------+ | +------------------------------>| IObject | | : | : +-----------+ | : V : | | : +-----------+ : | V +----------->| IObject | : | +-----------+ | : +-----------+ : | | ICookie |-------+ : | : V +-----------+ | : | : +-----------+ | +------------------------------>| IObject | +-----+-----+ : | : +-----------+ | | : | : | V | : V : | +-----------+ | : +-----------+ : | | ICookie |------------------------->| IObject | : | +-----------+ | : +-----------+ : | | V : | : V | +-----------+ : | : +-----------+ | | ICookie |-------------------------------->| IObject | | +-----------+ : | : +-----------+ V | : V : | +-----------+ | : +-----------+ : | | DCookie |------------------------->| DObject | : | +-----------+ | : +-----------+ : | | : : | +-------+-------+ : : | | | : : | V V : : V +-----------+ +-----------+ : : +-----------+ | DCookie | | DCookie |------------------------>| DObject | +-----------+ +-----------+ : : +-----------+ : : In the above illustration, ICookie and IObject represent indices and DCookie and DObject represent data storage objects. Indices may have representation in multiple caches, but currently, non-index objects may not. Objects of any type may also be entirely unrepresented. As far as the netfs API goes, the netfs is only actually permitted to see pointers to the cookies. The cookies themselves and any objects attached to those cookies are hidden from it. =============================== OBJECT MANAGEMENT STATE MACHINE =============================== Within FS-Cache, each active object is managed by its own individual state machine. The state for an object is kept in the fscache_object struct, in object->state. A cookie may point to a set of objects that are in different states. Each state has an action associated with it that is invoked when the machine wakes up in that state. There are four logical sets of states: (1) Preparation: states that wait for the parent objects to become ready. The representations are hierarchical, and it is expected that an object must be created or accessed with respect to its parent object. (2) Initialisation: states that perform lookups in the cache and validate what's found and that create on disk any missing metadata. (3) Normal running: states that allow netfs operations on objects to proceed and that update the state of objects. (4) Termination: states that detach objects from their netfs cookies, that delete objects from disk, that handle disk and system errors and that free up in-memory resources. In most cases, transitioning between states is in response to signalled events. When a state has finished processing, it will usually set the mask of events in which it is interested (object->event_mask) and relinquish the worker thread. Then when an event is raised (by calling fscache_raise_event()), if the event is not masked, the object will be queued for processing (by calling fscache_enqueue_object()). PROVISION OF CPU TIME --------------------- The work to be done by the various states is given CPU time by the threads of the slow work facility (see Documentation/slow-work.txt). This is used in preference to the workqueue facility because: (1) Threads may be completely occupied for very long periods of time by a particular work item. These state actions may be doing sequences of synchronous, journalled disk accesses (lookup, mkdir, create, setxattr, getxattr, truncate, unlink, rmdir, rename). (2) Threads may do little actual work, but may rather spend a lot of time sleeping on I/O. This means that single-threaded and 1-per-CPU-threaded workqueues don't necessarily have the right numbers of threads. LOCKING SIMPLIFICATION ---------------------- Because only one worker thread may be operating on any particular object's state machine at once, this simplifies the locking, particularly with respect to disconnecting the netfs's representation of a cache object (fscache_cookie) from the cache backend's representation (fscache_object) - which may be requested from either end. ================= THE SET OF STATES ================= The object state machine has a set of states that it can be in. There are preparation states in which the object sets itself up and waits for its parent object to transit to a state that allows access to its children: (1) State FSCACHE_OBJECT_INIT. Initialise the object and wait for the parent object to become active. In the cache, it is expected that it will not be possible to look an object up from the parent object, until that parent object itself has been looked up. There are initialisation states in which the object sets itself up and accesses disk for the object metadata: (2) State FSCACHE_OBJECT_LOOKING_UP. Look up the object on disk, using the parent as a starting point. FS-Cache expects the cache backend to probe the cache to see whether this object is represented there, and if it is, to see if it's valid (coherency management). The cache should call fscache_object_lookup_negative() to indicate lookup failure for whatever reason, and should call fscache_obtained_object() to indicate success. At the completion of lookup, FS-Cache will let the netfs go ahead with read operations, no matter whether the file is yet cached. If not yet cached, read operations will be immediately rejected with ENODATA until the first known page is uncached - as to that point there can be no data to be read out of the cache for that file that isn't currently also held in the pagecache. (3) State FSCACHE_OBJECT_CREATING. Create an object on disk, using the parent as a starting point. This happens if the lookup failed to find the object, or if the object's coherency data indicated what's on disk is out of date. In this state, FS-Cache expects the cache to create The cache should call fscache_obtained_object() if creation completes successfully, fscache_object_lookup_negative() otherwise. At the completion of creation, FS-Cache will start processing write operations the netfs has queued for an object. If creation failed, the write ops will be transparently discarded, and nothing recorded in the cache. There are some normal running states in which the object spends its time servicing netfs requests: (4) State FSCACHE_OBJECT_AVAILABLE. A transient state in which pending operations are started, child objects are permitted to advance from FSCACHE_OBJECT_INIT state, and temporary lookup data is freed. (5) State FSCACHE_OBJECT_ACTIVE. The normal running state. In this state, requests the netfs makes will be passed on to the cache. (6) State FSCACHE_OBJECT_UPDATING. The state machine comes here to update the object in the cache from the netfs's records. This involves updating the auxiliary data that is used to maintain coherency. And there are terminal states in which an object cleans itself up, deallocates memory and potentially deletes stuff from disk: (7) State FSCACHE_OBJECT_LC_DYING. The object comes here if it is dying because of a lookup or creation error. This would be due to a disk error or system error of some sort. Temporary data is cleaned up, and the parent is released. (8) State FSCACHE_OBJECT_DYING. The object comes here if it is dying due to an error, because its parent cookie has been relinquished by the netfs or because the cache is being withdrawn. Any child objects waiting on this one are given CPU time so that they too can destroy themselves. This object waits for all its children to go away before advancing to the next state. (9) State FSCACHE_OBJECT_ABORT_INIT. The object comes to this state if it was waiting on its parent in FSCACHE_OBJECT_INIT, but its parent died. The object will destroy itself so that the parent may proceed from the FSCACHE_OBJECT_DYING state. (10) State FSCACHE_OBJECT_RELEASING. (11) State FSCACHE_OBJECT_RECYCLING. The object comes to one of these two states when dying once it is rid of all its children, if it is dying because the netfs relinquished its cookie. In the first state, the cached data is expected to persist, and in the second it will be deleted. (12) State FSCACHE_OBJECT_WITHDRAWING. The object transits to this state if the cache decides it wants to withdraw the object from service, perhaps to make space, but also due to error or just because the whole cache is being withdrawn. (13) State FSCACHE_OBJECT_DEAD. The object transits to this state when the in-memory object record is ready to be deleted. The object processor shouldn't ever see an object in this state. THE SET OF EVENTS ----------------- There are a number of events that can be raised to an object state machine: (*) FSCACHE_OBJECT_EV_UPDATE The netfs requested that an object be updated. The state machine will ask the cache backend to update the object, and the cache backend will ask the netfs for details of the change through its cookie definition ops. (*) FSCACHE_OBJECT_EV_CLEARED This is signalled in two circumstances: (a) when an object's last child object is dropped and (b) when the last operation outstanding on an object is completed. This is used to proceed from the dying state. (*) FSCACHE_OBJECT_EV_ERROR This is signalled when an I/O error occurs during the processing of some object. (*) FSCACHE_OBJECT_EV_RELEASE (*) FSCACHE_OBJECT_EV_RETIRE These are signalled when the netfs relinquishes a cookie it was using. The event selected depends on whether the netfs asks for the backing object to be retired (deleted) or retained. (*) FSCACHE_OBJECT_EV_WITHDRAW This is signalled when the cache backend wants to withdraw an object. This means that the object will have to be detached from the netfs's cookie. Because the withdrawing releasing/retiring events are all handled by the object state machine, it doesn't matter if there's a collision with both ends trying to sever the connection at the same time. The state machine can just pick which one it wants to honour, and that effects the other. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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2868cbea72 |
FS-Cache: Bit waiting helpers
Add helpers for use with wait_on_bit(). Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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726dd7ff10 |
FS-Cache: Add netfs registration
Add functions to register and unregister a network filesystem or other client of the FS-Cache service. This allocates and releases the cookie representing the top-level index for a netfs, and makes it available to the netfs. If the FS-Cache facility is disabled, then the calls are optimised away at compile time. Note that whilst this patch may appear to work with FS-Cache enabled and a netfs attempting to use it, it will leak the cookie it allocates for the netfs as fscache_relinquish_cookie() is implemented in a later patch. This will cause the slab code to emit a warning when the module is removed. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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955d00917f |
FS-Cache: Provide a slab for cookie allocation
Provide a slab from which can be allocated the FS-Cache cookies that will be presented to the netfs. Also provide a slab constructor and a function to recursively discard a cookie and its ancestor chain. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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4c515dd47a |
FS-Cache: Add cache management
Implement the entry points by which a cache backend may initialise, add, declare an error upon and withdraw a cache. Further, an object is created in sysfs under which each cache added will get an object created: /sys/fs/fscache/<cachetag>/ All of this is described in Documentation/filesystems/caching/backend-api.txt added by a previous patch. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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0e04d4cefc |
FS-Cache: Add cache tag handling
Implement two features of FS-Cache: (1) The ability to request and release cache tags - names by which a cache may be known to a netfs, and thus selected for use. (2) An internal function by which a cache is selected by consulting the netfs, if the netfs wishes to be consulted. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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a6891645cf |
FS-Cache: Root index definition
Add a description of the root index of the cache for later patches to make use of. The root index is owned by FS-Cache itself. When a netfs requests caching facilities, FS-Cache will, if one doesn't already exist, create an entry in the root index with the key being the name of the netfs ("AFS" for example), and the auxiliary data holding the index structure version supplied by the netfs: FSDEF | +-----------+ | | NFS AFS [v=1] [v=1] If an entry with the appropriate name does already exist, the version is compared. If the version is different, the entire subtree from that entry will be discarded and a new entry created. The new entry will be an index, and a cookie referring to it will be passed to the netfs. This is then the root handle by which the netfs accesses the cache. It can create whatever objects it likes in that index, including further indices. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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7394daa8c6 |
FS-Cache: Add use of /proc and presentation of statistics
Make FS-Cache create its /proc interface and present various statistical information through it. Also provide the functions for updating this information. These features are enabled by: CONFIG_FSCACHE_PROC CONFIG_FSCACHE_STATS CONFIG_FSCACHE_HISTOGRAM The /proc directory for FS-Cache is also exported so that caching modules can add their own statistics there too. The FS-Cache module is loadable at this point, and the statistics files can be examined by userspace: cat /proc/fs/fscache/stats cat /proc/fs/fscache/histogram Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |
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David Howells
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06b3db1b9b |
FS-Cache: Add main configuration option, module entry points and debugging
Add the main configuration option, allowing FS-Cache to be selected; the module entry and exit functions and the debugging stuff used by these patches. The two configuration options added are: CONFIG_FSCACHE CONFIG_FSCACHE_DEBUG The first enables the facility, and the second makes the debugging statements enableable through the "debug" module parameter. The value of this parameter is a bitmask as described in: Documentation/filesystems/caching/fscache.txt The module can be loaded at this point, but all it will do at this point in the patch series is to start up the slow work facility and shut it down again. Signed-off-by: David Howells <dhowells@redhat.com> Acked-by: Steve Dickson <steved@redhat.com> Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Daire Byrne <Daire.Byrne@framestore.com> |