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fscache: Count data storage objects in a cache

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Count the data storage objects that are currently allocated in a cache.
This is used to pin certain cache structures until cache withdrawal is
complete.

Three helpers are provided to manage and make use of the count:

 (1) void fscache_count_object(struct fscache_cache *cache);

     This should be called by the cache backend to note that an object has
     been allocated and attached to the cache.

 (2) void fscache_uncount_object(struct fscache_cache *cache);

     This should be called by the backend to note that an object has been
     destroyed.  This sends a wakeup event that allows cache withdrawal to
     proceed if it was waiting for that object.

 (3) void fscache_wait_for_objects(struct fscache_cache *cache);

     This can be used by the backend to wait for all outstanding cache
     object to be destroyed.

Each cache's counter is displayed as part of /proc/fs/fscache/caches.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819608594.215744.1812706538117388252.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906911646.143852.168184059935530127.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967111846.1823006.9868154941573671255.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021516219.640689.4934796654308958158.stgit@warthog.procyon.org.uk/ # v4
This commit is contained in:
David Howells 2021-11-11 23:14:29 +00:00
parent d64f4554dd
commit cdf262f294
2 changed files with 41 additions and 0 deletions
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2
fs/fscache/cache.c
View File

@ -13,6 +13,8 @@
static LIST_HEAD(fscache_caches);
DECLARE_RWSEM(fscache_addremove_sem);
EXPORT_SYMBOL(fscache_addremove_sem);
DECLARE_WAIT_QUEUE_HEAD(fscache_clearance_waiters);
EXPORT_SYMBOL(fscache_clearance_waiters);
static atomic_t fscache_cache_debug_id;

39
include/linux/fscache-cache.h
View File

@ -76,6 +76,7 @@ struct fscache_cache_ops {
};
extern struct workqueue_struct *fscache_wq;
extern wait_queue_head_t fscache_clearance_waiters;
/*
* out-of-line cache backend functions
@ -140,4 +141,42 @@ static inline struct fscache_cookie *fscache_cres_cookie(struct netfs_cache_reso
return cres->cache_priv;
}
/**
* fscache_count_object - Tell fscache that an object has been added
* @cache: The cache to account to
*
* Tell fscache that an object has been added to the cache. This prevents the
* cache from tearing down the cache structure until the object is uncounted.
*/
static inline void fscache_count_object(struct fscache_cache *cache)
{
atomic_inc(&cache->object_count);
}
/**
* fscache_uncount_object - Tell fscache that an object has been removed
* @cache: The cache to account to
*
* Tell fscache that an object has been removed from the cache and will no
* longer be accessed. After this point, the cache cookie may be destroyed.
*/
static inline void fscache_uncount_object(struct fscache_cache *cache)
{
if (atomic_dec_and_test(&cache->object_count))
wake_up_all(&fscache_clearance_waiters);
}
/**
* fscache_wait_for_objects - Wait for all objects to be withdrawn
* @cache: The cache to query
*
* Wait for all extant objects in a cache to finish being withdrawn
* and go away.
*/
static inline void fscache_wait_for_objects(struct fscache_cache *cache)
{
wait_event(fscache_clearance_waiters,
atomic_read(&cache->object_count) == 0);
}
#endif /* _LINUX_FSCACHE_CACHE_H */