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92a714d727
An issue can occur between write-streaming (storing dirty data in partial
non-uptodate pages) and a cachefiles object being culled to make space.
The problem occurs because the cache object is only marked in use while
there are files open using it. Once it has been released, it can be culled
and the cookie marked disabled.
At this point, a streaming write is permitted to occur (if the cache is
active, we require pages to be prefetched and cached), but the cache can
become active again before this gets flushed out - and then two effects can
occur:
(1) The cache may be asked to write out a region that's less than its DIO
block size (assumed by cachefiles to be PAGE_SIZE) - and this causes
one of two debugging statements to be emitted.
(2) netfs_how_to_modify() gets confused because it sees a page that isn't
allowed to be non-uptodate being uptodate and tries to prefetch it -
leading to a warning that PG_fscache is set twice.
Fix this by the following means:
(1) Add a netfs_inode flag to disallow write-streaming to an inode and set
it if we ever do local caching of that inode. It remains set for the
lifetime of that inode - even if the cookie becomes disabled.
(2) If the no-write-streaming flag is set, then make netfs_how_to_modify()
always want to prefetch instead.
(3) If netfs_how_to_modify() decides it wants to prefetch a folio, but
that folio has write-streamed data in it, then it requires the folio
be flushed first.
(4) Export a counter of the number of times we wanted to prefetch a
non-uptodate page, but found it had write-streamed data in it.
(5) Export a counter of the number of times we cancelled a write to the
cache because it didn't DIO align and remove the debug statements.
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-erofs@lists.ozlabs.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
208 lines
6.8 KiB
C
208 lines
6.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/* General filesystem caching backing cache interface
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*
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* Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*
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* NOTE!!! See:
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*
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* Documentation/filesystems/caching/backend-api.rst
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*
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* for a description of the cache backend interface declared here.
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*/
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#ifndef _LINUX_FSCACHE_CACHE_H
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#define _LINUX_FSCACHE_CACHE_H
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#include <linux/fscache.h>
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enum fscache_cache_trace;
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enum fscache_cookie_trace;
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enum fscache_access_trace;
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enum fscache_cache_state {
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FSCACHE_CACHE_IS_NOT_PRESENT, /* No cache is present for this name */
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FSCACHE_CACHE_IS_PREPARING, /* A cache is preparing to come live */
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FSCACHE_CACHE_IS_ACTIVE, /* Attached cache is active and can be used */
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FSCACHE_CACHE_GOT_IOERROR, /* Attached cache stopped on I/O error */
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FSCACHE_CACHE_IS_WITHDRAWN, /* Attached cache is being withdrawn */
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#define NR__FSCACHE_CACHE_STATE (FSCACHE_CACHE_IS_WITHDRAWN + 1)
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};
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/*
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* Cache cookie.
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*/
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struct fscache_cache {
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const struct fscache_cache_ops *ops;
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struct list_head cache_link; /* Link in cache list */
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void *cache_priv; /* Private cache data (or NULL) */
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refcount_t ref;
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atomic_t n_volumes; /* Number of active volumes; */
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atomic_t n_accesses; /* Number of in-progress accesses on the cache */
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atomic_t object_count; /* no. of live objects in this cache */
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unsigned int debug_id;
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enum fscache_cache_state state;
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char *name;
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};
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/*
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* cache operations
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*/
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struct fscache_cache_ops {
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/* name of cache provider */
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const char *name;
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/* Acquire a volume */
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void (*acquire_volume)(struct fscache_volume *volume);
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/* Free the cache's data attached to a volume */
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void (*free_volume)(struct fscache_volume *volume);
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/* Look up a cookie in the cache */
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bool (*lookup_cookie)(struct fscache_cookie *cookie);
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/* Withdraw an object without any cookie access counts held */
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void (*withdraw_cookie)(struct fscache_cookie *cookie);
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/* Change the size of a data object */
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void (*resize_cookie)(struct netfs_cache_resources *cres,
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loff_t new_size);
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/* Invalidate an object */
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bool (*invalidate_cookie)(struct fscache_cookie *cookie);
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/* Begin an operation for the netfs lib */
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bool (*begin_operation)(struct netfs_cache_resources *cres,
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enum fscache_want_state want_state);
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/* Prepare to write to a live cache object */
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void (*prepare_to_write)(struct fscache_cookie *cookie);
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};
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extern struct workqueue_struct *fscache_wq;
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extern wait_queue_head_t fscache_clearance_waiters;
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/*
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* out-of-line cache backend functions
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*/
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extern struct rw_semaphore fscache_addremove_sem;
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extern struct fscache_cache *fscache_acquire_cache(const char *name);
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extern void fscache_relinquish_cache(struct fscache_cache *cache);
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extern int fscache_add_cache(struct fscache_cache *cache,
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const struct fscache_cache_ops *ops,
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void *cache_priv);
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extern void fscache_withdraw_cache(struct fscache_cache *cache);
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extern void fscache_withdraw_volume(struct fscache_volume *volume);
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extern void fscache_withdraw_cookie(struct fscache_cookie *cookie);
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extern void fscache_io_error(struct fscache_cache *cache);
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extern void fscache_end_volume_access(struct fscache_volume *volume,
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struct fscache_cookie *cookie,
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enum fscache_access_trace why);
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extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
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enum fscache_cookie_trace where);
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extern void fscache_put_cookie(struct fscache_cookie *cookie,
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enum fscache_cookie_trace where);
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extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
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enum fscache_access_trace why);
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extern void fscache_cookie_lookup_negative(struct fscache_cookie *cookie);
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extern void fscache_resume_after_invalidation(struct fscache_cookie *cookie);
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extern void fscache_caching_failed(struct fscache_cookie *cookie);
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extern bool fscache_wait_for_operation(struct netfs_cache_resources *cred,
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enum fscache_want_state state);
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/**
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* fscache_cookie_state - Read the state of a cookie
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* @cookie: The cookie to query
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*
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* Get the state of a cookie, imposing an ordering between the cookie contents
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* and the state value. Paired with fscache_set_cookie_state().
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*/
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static inline
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enum fscache_cookie_state fscache_cookie_state(struct fscache_cookie *cookie)
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{
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return smp_load_acquire(&cookie->state);
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}
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/**
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* fscache_get_key - Get a pointer to the cookie key
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* @cookie: The cookie to query
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*
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* Return a pointer to the where a cookie's key is stored.
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*/
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static inline void *fscache_get_key(struct fscache_cookie *cookie)
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{
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if (cookie->key_len <= sizeof(cookie->inline_key))
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return cookie->inline_key;
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else
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return cookie->key;
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}
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static inline struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_resources *cres)
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{
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return cres->cache_priv;
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}
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/**
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* fscache_count_object - Tell fscache that an object has been added
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* @cache: The cache to account to
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*
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* Tell fscache that an object has been added to the cache. This prevents the
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* cache from tearing down the cache structure until the object is uncounted.
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*/
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static inline void fscache_count_object(struct fscache_cache *cache)
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{
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atomic_inc(&cache->object_count);
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}
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/**
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* fscache_uncount_object - Tell fscache that an object has been removed
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* @cache: The cache to account to
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*
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* Tell fscache that an object has been removed from the cache and will no
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* longer be accessed. After this point, the cache cookie may be destroyed.
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*/
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static inline void fscache_uncount_object(struct fscache_cache *cache)
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{
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if (atomic_dec_and_test(&cache->object_count))
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wake_up_all(&fscache_clearance_waiters);
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}
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/**
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* fscache_wait_for_objects - Wait for all objects to be withdrawn
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* @cache: The cache to query
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*
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* Wait for all extant objects in a cache to finish being withdrawn
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* and go away.
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*/
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static inline void fscache_wait_for_objects(struct fscache_cache *cache)
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{
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wait_event(fscache_clearance_waiters,
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atomic_read(&cache->object_count) == 0);
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}
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#ifdef CONFIG_FSCACHE_STATS
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extern atomic_t fscache_n_read;
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extern atomic_t fscache_n_write;
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extern atomic_t fscache_n_no_write_space;
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extern atomic_t fscache_n_no_create_space;
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extern atomic_t fscache_n_culled;
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extern atomic_t fscache_n_dio_misfit;
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#define fscache_count_read() atomic_inc(&fscache_n_read)
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#define fscache_count_write() atomic_inc(&fscache_n_write)
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#define fscache_count_no_write_space() atomic_inc(&fscache_n_no_write_space)
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#define fscache_count_no_create_space() atomic_inc(&fscache_n_no_create_space)
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#define fscache_count_culled() atomic_inc(&fscache_n_culled)
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#define fscache_count_dio_misfit() atomic_inc(&fscache_n_dio_misfit)
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#else
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#define fscache_count_read() do {} while(0)
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#define fscache_count_write() do {} while(0)
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#define fscache_count_no_write_space() do {} while(0)
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#define fscache_count_no_create_space() do {} while(0)
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#define fscache_count_culled() do {} while(0)
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#define fscache_count_dio_misfit() do {} while(0)
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#endif
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#endif /* _LINUX_FSCACHE_CACHE_H */
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