kernel/linux.git/include/linux/fscache-cache.h, branch v6.19.11

netfs, fscache: export fscache_put_volume() and add fscache_try_get_volume()

2024-07-03T08:36:14+00:00

Export fscache_put_volume() and add fscache_try_get_volume() helper function to allow cachefiles to get/put fscache_volume via linux/fscache-cache.h. Signed-off-by: Baokun Li Link: https://lore.kernel.org/r/20240628062930.2467993-2-libaokun@huaweicloud.com Signed-off-by: Christian Brauner

netfs: Fix interaction between write-streaming and cachefiles culling

2024-01-05T15:42:25+00:00

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 Signed-off-by: David Howells cc: Jeff Layton cc: linux-cachefs@redhat.com cc: linux-erofs@lists.ozlabs.org cc: linux-fsdevel@vger.kernel.org cc: linux-mm@kvack.org

fscache, cachefiles: Display stat of culling events

2022-01-07T13:43:18+00:00

Add a stat counter of culling events whereby the cache backend culls a file to make space (when asked by cachefilesd in this case) and display in /proc/fs/fscache/stats. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819654165.215744.3797804661644212436.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906961387.143852.9291157239960289090.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967168266.1823006.14436200166581605746.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021567619.640689.4339228906248763197.stgit@warthog.procyon.org.uk/ # v4

fscache, cachefiles: Display stats of no-space events

2022-01-07T13:43:13+00:00

Add stat counters of no-space events that caused caching not to happen and display in /proc/fs/fscache/stats. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819653216.215744.17210522251617386509.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906958369.143852.7257100711818401748.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967166917.1823006.14842444049198947892.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021566184.640689.4417328329632709265.stgit@warthog.procyon.org.uk/ # v4

fscache: Provide a function to resize a cookie

2022-01-07T13:40:33+00:00

Provide a function to change the size of the storage attached to a cookie, to match the size of the file being cached when it's changed by truncate or fallocate: void fscache_resize_cookie(struct fscache_cookie *cookie, loff_t new_size); This acts synchronously and is expected to run under the inode lock of the caller. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819621839.215744.7895597119803515402.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906922387.143852.16394459879816147793.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967128998.1823006.10740669081985775576.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021527861.640689.3466382085497236267.stgit@warthog.procyon.org.uk/ # v4

fscache: Provide read/write stat counters for the cache

2022-01-07T09:22:19+00:00

Provide read/write stat counters for the cache backend to use. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819609532.215744.10821082637727410554.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906912598.143852.12960327989649429069.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967113830.1823006.3222957649202368162.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021517502.640689.6077928311710357342.stgit@warthog.procyon.org.uk/ # v4

fscache: Count data storage objects in a cache

2022-01-07T09:22:19+00:00

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 Reviewed-by: Jeff Layton 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

fscache: Provide a means to begin an operation

2022-01-07T09:22:19+00:00

Provide a function to begin a read operation: int fscache_begin_read_operation( struct netfs_cache_resources *cres, struct fscache_cookie *cookie) This is primarily intended to be called by network filesystems on behalf of netfslib, but may also be called to use the I/O access functions directly. It attaches the resources required by the cache to cres struct from the supplied cookie. This holds access to the cache behind the cookie for the duration of the operation and forces cache withdrawal and cookie invalidation to perform synchronisation on the operation. cres->inval_counter is set from the cookie at this point so that it can be compared at the end of the operation. Note that this does not guarantee that the cache state is fully set up and able to perform I/O immediately; looking up and creation may be left in progress in the background. The operations intended to be called by the network filesystem, such as reading and writing, are expected to wait for the cookie to move to the correct state. This will, however, potentially sleep, waiting for a certain minimum state to be set or for operations such as invalidate to advance far enough that I/O can resume. Also provide a function for the cache to call to wait for the cache object to get to a state where it can be used for certain things: bool fscache_wait_for_operation(struct netfs_cache_resources *cres, enum fscache_want_stage stage); This looks at the cache resources provided by the begin function and waits for them to get to an appropriate stage. There's a choice of wanting just some parameters (FSCACHE_WANT_PARAM) or the ability to do I/O (FSCACHE_WANT_READ or FSCACHE_WANT_WRITE). Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819603692.215744.146724961588817028.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906910672.143852.13856103384424986357.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967110245.1823006.2239170567540431836.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021513617.640689.16627329360866150606.stgit@warthog.procyon.org.uk/ # v4

fscache: Implement cookie invalidation

2022-01-07T09:22:19+00:00

Add a function to invalidate the cache behind a cookie: void fscache_invalidate(struct fscache_cookie *cookie, const void *aux_data, loff_t size, unsigned int flags) This causes any cached data for the specified cookie to be discarded. If the cookie is marked as being in use, a new cache object will be created if possible and future I/O will use that instead. In-flight I/O should be abandoned (writes) or reconsidered (reads). Each time it is called cookie->inval_counter is incremented and this can be used to detect invalidation at the end of an I/O operation. The coherency data attached to the cookie can be updated and the cookie size should be reset. One flag is available, FSCACHE_INVAL_DIO_WRITE, which should be used to indicate invalidation due to a DIO write on a file. This will temporarily disable caching for this cookie. Changes ======= ver #2: - Should only change to inval state if can get access to cache. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/163819602231.215744.11206598147269491575.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906909707.143852.18056070560477964891.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967107447.1823006.5945029409592119962.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021512640.640689.11418616313147754172.stgit@warthog.procyon.org.uk/ # v4

fscache: Implement simple cookie state machine

2022-01-07T09:22:19+00:00

Implement a very simple cookie state machine to handle lookup, invalidation, withdrawal, relinquishment and, to be added later, commit on LRU discard. Three cache methods are provided: ->lookup_cookie() to look up and, if necessary, create a data storage object; ->withdraw_cookie() to free the resources associated with that object and potentially delete it; and ->prepare_to_write(), to do prepare for changes to the cached data to be modified locally. Changes ======= ver #3: - Fix a race between LRU discard and relinquishment whereby the former would override the latter and thus the latter would never happen[1]. ver #2: - Don't hold n_accesses elevated whilst cache is bound to a cookie, but rather add a flag that prevents the state machine from being queued when n_accesses reaches 0. Signed-off-by: David Howells Reviewed-by: Jeff Layton cc: linux-cachefs@redhat.com Link: https://lore.kernel.org/r/599331.1639410068@warthog.procyon.org.uk/ [1] Link: https://lore.kernel.org/r/163819599657.215744.15799615296912341745.stgit@warthog.procyon.org.uk/ # v1 Link: https://lore.kernel.org/r/163906903925.143852.1805855338154353867.stgit@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/163967105456.1823006.14730395299835841776.stgit@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/164021510706.640689.7961423370243272583.stgit@warthog.procyon.org.uk/ # v4