[PATCH v2 21/67] fscache: Count data storage objects in a cache
From: David Howells <dhowells@redhat.com>
Date: 2021-12-09 16:58:56
Also in:
ceph-devel, linux-cifs, linux-fsdevel, lkml
Subsystem:
filesystems (vfs and infrastructure), filesystems [netfs library], the rest · Maintainers:
Alexander Viro, Christian Brauner, David Howells, Paulo Alcantara, Linus Torvalds
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>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819608594.215744.1812706538117388252.stgit@warthog.procyon.org.uk/ (local) # v1
---
fs/fscache/cache.c | 2 ++
include/linux/fscache-cache.h | 39 +++++++++++++++++++++++++++++++++++++++
2 files changed, 41 insertions(+)
diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
index 25eac61f1c29..2749933852a9 100644
--- a/fs/fscache/cache.c
+++ b/fs/fscache/cache.c@@ -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;
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index 566497cf5f13..337335d7a5e2 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h@@ -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 */