Commit cdf262f2 authored by David Howells's avatar David Howells
Browse files

fscache: Count data storage objects in a cache 



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: default avatarDavid Howells <dhowells@redhat.com>
Reviewed-by: default avatarJeff 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
parent d64f4554

fs/fscache/cache.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

include/linux/fscache-cache.h

+39 −0
Original line number Diff line number Diff line
@@ -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 */