linux/fs/fscache/io.c
David Howells 16f2f4e679 nfs: Implement cache I/O by accessing the cache directly
Move NFS to using fscache DIO API instead of the old upstream I/O API as
that has been removed.  This is a stopgap solution as the intention is that
at sometime in the future, the cache will move to using larger blocks and
won't be able to store individual pages in order to deal with the potential
for data corruption due to the backing filesystem being able insert/remove
bridging blocks of zeros into its extent list[1].

NFS then reads and writes cache pages synchronously and one page at a time.

The preferred change would be to use the netfs lib, but the new I/O API can
be used directly.  It's just that as the cache now needs to track data for
itself, caching blocks may exceed page size...

This code is somewhat borrowed from my "fallback I/O" patchset[2].

Changes
=======
ver #3:
 - Restore lost =n fallback for nfs_fscache_release_page()[2].

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
cc: Trond Myklebust <trond.myklebust@hammerspace.com>
cc: Anna Schumaker <anna.schumaker@netapp.com>
cc: linux-nfs@vger.kernel.org
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/YO17ZNOcq+9PajfQ@mit.edu [1]
Link: https://lore.kernel.org/r/202112100957.2oEDT20W-lkp@intel.com/ [2]
Link: https://lore.kernel.org/r/163189108292.2509237.12615909591150927232.stgit@warthog.procyon.org.uk/ [2]
Link: https://lore.kernel.org/r/163906981318.143852.17220018647843475985.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967184451.1823006.6450645559828329590.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021577632.640689.11069627070150063812.stgit@warthog.procyon.org.uk/ # v4
2022-01-10 11:53:25 +00:00

327 lines
8.8 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* Cache data I/O routines
*
* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#define FSCACHE_DEBUG_LEVEL OPERATION
#include <linux/fscache-cache.h>
#include <linux/uio.h>
#include <linux/bvec.h>
#include <linux/slab.h>
#include <linux/uio.h>
#include "internal.h"
/**
* fscache_wait_for_operation - Wait for an object become accessible
* @cres: The cache resources for the operation being performed
* @want_state: The minimum state the object must be at
*
* See if the target cache object is at the specified minimum state of
* accessibility yet, and if not, wait for it.
*/
bool fscache_wait_for_operation(struct netfs_cache_resources *cres,
enum fscache_want_state want_state)
{
struct fscache_cookie *cookie = fscache_cres_cookie(cres);
enum fscache_cookie_state state;
again:
if (!fscache_cache_is_live(cookie->volume->cache)) {
_leave(" [broken]");
return false;
}
state = fscache_cookie_state(cookie);
_enter("c=%08x{%u},%x", cookie->debug_id, state, want_state);
switch (state) {
case FSCACHE_COOKIE_STATE_CREATING:
case FSCACHE_COOKIE_STATE_INVALIDATING:
if (want_state == FSCACHE_WANT_PARAMS)
goto ready; /* There can be no content */
fallthrough;
case FSCACHE_COOKIE_STATE_LOOKING_UP:
case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
wait_var_event(&cookie->state,
fscache_cookie_state(cookie) != state);
goto again;
case FSCACHE_COOKIE_STATE_ACTIVE:
goto ready;
case FSCACHE_COOKIE_STATE_DROPPED:
case FSCACHE_COOKIE_STATE_RELINQUISHING:
default:
_leave(" [not live]");
return false;
}
ready:
if (!cres->cache_priv2)
return cookie->volume->cache->ops->begin_operation(cres, want_state);
return true;
}
EXPORT_SYMBOL(fscache_wait_for_operation);
/*
* Begin an I/O operation on the cache, waiting till we reach the right state.
*
* Attaches the resources required to the operation resources record.
*/
static int fscache_begin_operation(struct netfs_cache_resources *cres,
struct fscache_cookie *cookie,
enum fscache_want_state want_state,
enum fscache_access_trace why)
{
enum fscache_cookie_state state;
long timeo;
bool once_only = false;
cres->ops = NULL;
cres->cache_priv = cookie;
cres->cache_priv2 = NULL;
cres->debug_id = cookie->debug_id;
cres->inval_counter = cookie->inval_counter;
if (!fscache_begin_cookie_access(cookie, why))
return -ENOBUFS;
again:
spin_lock(&cookie->lock);
state = fscache_cookie_state(cookie);
_enter("c=%08x{%u},%x", cookie->debug_id, state, want_state);
switch (state) {
case FSCACHE_COOKIE_STATE_LOOKING_UP:
case FSCACHE_COOKIE_STATE_LRU_DISCARDING:
case FSCACHE_COOKIE_STATE_INVALIDATING:
goto wait_for_file_wrangling;
case FSCACHE_COOKIE_STATE_CREATING:
if (want_state == FSCACHE_WANT_PARAMS)
goto ready; /* There can be no content */
goto wait_for_file_wrangling;
case FSCACHE_COOKIE_STATE_ACTIVE:
goto ready;
case FSCACHE_COOKIE_STATE_DROPPED:
case FSCACHE_COOKIE_STATE_RELINQUISHING:
WARN(1, "Can't use cookie in state %u\n", cookie->state);
goto not_live;
default:
goto not_live;
}
ready:
spin_unlock(&cookie->lock);
if (!cookie->volume->cache->ops->begin_operation(cres, want_state))
goto failed;
return 0;
wait_for_file_wrangling:
spin_unlock(&cookie->lock);
trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
atomic_read(&cookie->n_accesses),
fscache_access_io_wait);
timeo = wait_var_event_timeout(&cookie->state,
fscache_cookie_state(cookie) != state, 20 * HZ);
if (timeo <= 1 && !once_only) {
pr_warn("%s: cookie state change wait timed out: cookie->state=%u state=%u",
__func__, fscache_cookie_state(cookie), state);
fscache_print_cookie(cookie, 'O');
once_only = true;
}
goto again;
not_live:
spin_unlock(&cookie->lock);
failed:
cres->cache_priv = NULL;
cres->ops = NULL;
fscache_end_cookie_access(cookie, fscache_access_io_not_live);
_leave(" = -ENOBUFS");
return -ENOBUFS;
}
int __fscache_begin_read_operation(struct netfs_cache_resources *cres,
struct fscache_cookie *cookie)
{
return fscache_begin_operation(cres, cookie, FSCACHE_WANT_PARAMS,
fscache_access_io_read);
}
EXPORT_SYMBOL(__fscache_begin_read_operation);
int __fscache_begin_write_operation(struct netfs_cache_resources *cres,
struct fscache_cookie *cookie)
{
return fscache_begin_operation(cres, cookie, FSCACHE_WANT_PARAMS,
fscache_access_io_write);
}
EXPORT_SYMBOL(__fscache_begin_write_operation);
/**
* fscache_set_page_dirty - Mark page dirty and pin a cache object for writeback
* @page: The page being dirtied
* @cookie: The cookie referring to the cache object
*
* Set the dirty flag on a page and pin an in-use cache object in memory when
* dirtying a page so that writeback can later write to it. This is intended
* to be called from the filesystem's ->set_page_dirty() method.
*
* Returns 1 if PG_dirty was set on the page, 0 otherwise.
*/
int fscache_set_page_dirty(struct page *page, struct fscache_cookie *cookie)
{
struct inode *inode = page->mapping->host;
bool need_use = false;
_enter("");
if (!__set_page_dirty_nobuffers(page))
return 0;
if (!fscache_cookie_valid(cookie))
return 1;
if (!(inode->i_state & I_PINNING_FSCACHE_WB)) {
spin_lock(&inode->i_lock);
if (!(inode->i_state & I_PINNING_FSCACHE_WB)) {
inode->i_state |= I_PINNING_FSCACHE_WB;
need_use = true;
}
spin_unlock(&inode->i_lock);
if (need_use)
fscache_use_cookie(cookie, true);
}
return 1;
}
EXPORT_SYMBOL(fscache_set_page_dirty);
struct fscache_write_request {
struct netfs_cache_resources cache_resources;
struct address_space *mapping;
loff_t start;
size_t len;
bool set_bits;
netfs_io_terminated_t term_func;
void *term_func_priv;
};
void __fscache_clear_page_bits(struct address_space *mapping,
loff_t start, size_t len)
{
pgoff_t first = start / PAGE_SIZE;
pgoff_t last = (start + len - 1) / PAGE_SIZE;
struct page *page;
if (len) {
XA_STATE(xas, &mapping->i_pages, first);
rcu_read_lock();
xas_for_each(&xas, page, last) {
end_page_fscache(page);
}
rcu_read_unlock();
}
}
EXPORT_SYMBOL(__fscache_clear_page_bits);
/*
* Deal with the completion of writing the data to the cache.
*/
static void fscache_wreq_done(void *priv, ssize_t transferred_or_error,
bool was_async)
{
struct fscache_write_request *wreq = priv;
fscache_clear_page_bits(fscache_cres_cookie(&wreq->cache_resources),
wreq->mapping, wreq->start, wreq->len,
wreq->set_bits);
if (wreq->term_func)
wreq->term_func(wreq->term_func_priv, transferred_or_error,
was_async);
fscache_end_operation(&wreq->cache_resources);
kfree(wreq);
}
void __fscache_write_to_cache(struct fscache_cookie *cookie,
struct address_space *mapping,
loff_t start, size_t len, loff_t i_size,
netfs_io_terminated_t term_func,
void *term_func_priv,
bool cond)
{
struct fscache_write_request *wreq;
struct netfs_cache_resources *cres;
struct iov_iter iter;
int ret = -ENOBUFS;
if (len == 0)
goto abandon;
_enter("%llx,%zx", start, len);
wreq = kzalloc(sizeof(struct fscache_write_request), GFP_NOFS);
if (!wreq)
goto abandon;
wreq->mapping = mapping;
wreq->start = start;
wreq->len = len;
wreq->set_bits = cond;
wreq->term_func = term_func;
wreq->term_func_priv = term_func_priv;
cres = &wreq->cache_resources;
if (fscache_begin_operation(cres, cookie, FSCACHE_WANT_WRITE,
fscache_access_io_write) < 0)
goto abandon_free;
ret = cres->ops->prepare_write(cres, &start, &len, i_size, false);
if (ret < 0)
goto abandon_end;
/* TODO: Consider clearing page bits now for space the write isn't
* covering. This is more complicated than it appears when THPs are
* taken into account.
*/
iov_iter_xarray(&iter, WRITE, &mapping->i_pages, start, len);
fscache_write(cres, start, &iter, fscache_wreq_done, wreq);
return;
abandon_end:
return fscache_wreq_done(wreq, ret, false);
abandon_free:
kfree(wreq);
abandon:
fscache_clear_page_bits(cookie, mapping, start, len, cond);
if (term_func)
term_func(term_func_priv, ret, false);
}
EXPORT_SYMBOL(__fscache_write_to_cache);
/*
* Change the size of a backing object.
*/
void __fscache_resize_cookie(struct fscache_cookie *cookie, loff_t new_size)
{
struct netfs_cache_resources cres;
trace_fscache_resize(cookie, new_size);
if (fscache_begin_operation(&cres, cookie, FSCACHE_WANT_WRITE,
fscache_access_io_resize) == 0) {
fscache_stat(&fscache_n_resizes);
set_bit(FSCACHE_COOKIE_NEEDS_UPDATE, &cookie->flags);
/* We cannot defer a resize as we need to do it inside the
* netfs's inode lock so that we're serialised with respect to
* writes.
*/
cookie->volume->cache->ops->resize_cookie(&cres, new_size);
fscache_end_operation(&cres);
} else {
fscache_stat(&fscache_n_resizes_null);
}
}
EXPORT_SYMBOL(__fscache_resize_cookie);