From: David Howells <dhowells@redhat.com>
To: linux-cachefs@redhat.com
Cc: Jeff Layton <jlayton@kernel.org>,
dhowells@redhat.com, Trond Myklebust <trondmy@hammerspace.com>,
Anna Schumaker <anna.schumaker@netapp.com>,
Steve French <sfrench@samba.org>,
Dominique Martinet <asmadeus@codewreck.org>,
Jeff Layton <jlayton@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Omar Sandoval <osandov@osandov.com>,
JeffleXu <jefflexu@linux.alibaba.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
v9fs-developer@lists.sourceforge.net,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v4 13/68] fscache: Implement cookie-level access helpers
Date: Wed, 22 Dec 2021 23:17:10 +0000 [thread overview]
Message-ID: <164021503063.640689.8870918985269528670.stgit@warthog.procyon.org.uk> (raw)
In-Reply-To: <164021479106.640689.17404516570194656552.stgit@warthog.procyon.org.uk>
Add a number of helper functions to manage access to a cookie, pinning the
cache object in place for the duration to prevent cache withdrawal from
removing it:
(1) void fscache_init_access_gate(struct fscache_cookie *cookie);
This function initialises the access count when a cache binds to a
cookie. An extra ref is taken on the access count to prevent wakeups
while the cache is active. We're only interested in the wakeup when a
cookie is being withdrawn and we're waiting for it to quiesce - at
which point the counter will be decremented before the wait.
The FSCACHE_COOKIE_NACC_ELEVATED flag is set on the cookie to keep
track of the extra ref in order to handle a race between
relinquishment and withdrawal both trying to drop the extra ref.
(2) bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
This function attempts to begin access upon a cookie, pinning it in
place if it's cached. If successful, it returns true and leaves a the
access count incremented.
(3) void fscache_end_cookie_access(struct fscache_cookie *cookie,
enum fscache_access_trace why);
This function drops the access count obtained by (2), permitting
object withdrawal to take place when it reaches zero.
A tracepoint is provided to track changes to the access counter on a
cookie.
Changes
=======
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 <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/r/163819595085.215744.1706073049250505427.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906895313.143852.10141619544149102193.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967095980.1823006.1133648159424418877.stgit@warthog.procyon.org.uk/ # v3
---
fs/fscache/cookie.c | 98 ++++++++++++++++++++++++++++++++++++++++
fs/fscache/internal.h | 3 +
fs/fscache/main.c | 1
include/linux/fscache-cache.h | 2 +
include/trace/events/fscache.h | 29 ++++++++++++
5 files changed, 133 insertions(+)
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 438b0098aa73..04d2127bd354 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -62,6 +62,104 @@ static void fscache_free_cookie(struct fscache_cookie *cookie)
kmem_cache_free(fscache_cookie_jar, cookie);
}
+/*
+ * Initialise the access gate on a cookie by setting a flag to prevent the
+ * state machine from being queued when the access counter transitions to 0.
+ * We're only interested in this when we withdraw caching services from the
+ * cookie.
+ */
+static void fscache_init_access_gate(struct fscache_cookie *cookie)
+{
+ int n_accesses;
+
+ n_accesses = atomic_read(&cookie->n_accesses);
+ trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
+ n_accesses, fscache_access_cache_pin);
+ set_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags);
+}
+
+/**
+ * fscache_end_cookie_access - Unpin a cache at the end of an access.
+ * @cookie: A data file cookie
+ * @why: An indication of the circumstances of the access for tracing
+ *
+ * Unpin a cache cookie after we've accessed it and bring a deferred
+ * relinquishment or withdrawal state into effect.
+ *
+ * The @why indicator is provided for tracing purposes.
+ */
+void fscache_end_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ smp_mb__before_atomic();
+ n_accesses = atomic_dec_return(&cookie->n_accesses);
+ trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
+ n_accesses, why);
+ if (n_accesses == 0 &&
+ !test_bit(FSCACHE_COOKIE_NO_ACCESS_WAKE, &cookie->flags)) {
+ // PLACEHOLDER: Need to poke the state machine
+ }
+}
+EXPORT_SYMBOL(fscache_end_cookie_access);
+
+/*
+ * Pin the cache behind a cookie so that we can access it.
+ */
+static void __fscache_begin_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why)
+{
+ int n_accesses;
+
+ n_accesses = atomic_inc_return(&cookie->n_accesses);
+ smp_mb__after_atomic(); /* (Future) read state after is-caching.
+ * Reread n_accesses after is-caching
+ */
+ trace_fscache_access(cookie->debug_id, refcount_read(&cookie->ref),
+ n_accesses, why);
+}
+
+/**
+ * fscache_begin_cookie_access - Pin a cache so data can be accessed
+ * @cookie: A data file cookie
+ * @why: An indication of the circumstances of the access for tracing
+ *
+ * Attempt to pin the cache to prevent it from going away whilst we're
+ * accessing data and returns true if successful. This works as follows:
+ *
+ * (1) If the cookie is not being cached (ie. FSCACHE_COOKIE_IS_CACHING is not
+ * set), we return false to indicate access was not permitted.
+ *
+ * (2) If the cookie is being cached, we increment its n_accesses count and
+ * then recheck the IS_CACHING flag, ending the access if it got cleared.
+ *
+ * (3) When we end the access, we decrement the cookie's n_accesses and wake
+ * up the any waiters if it reaches 0.
+ *
+ * (4) Whilst the cookie is actively being cached, its n_accesses is kept
+ * artificially incremented to prevent wakeups from happening.
+ *
+ * (5) When the cache is taken offline or if the cookie is culled, the flag is
+ * cleared to prevent new accesses, the cookie's n_accesses is decremented
+ * and we wait for it to become 0.
+ *
+ * The @why indicator are merely provided for tracing purposes.
+ */
+bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why)
+{
+ if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags))
+ return false;
+ __fscache_begin_cookie_access(cookie, why);
+ if (!test_bit(FSCACHE_COOKIE_IS_CACHING, &cookie->flags) ||
+ !fscache_cache_is_live(cookie->volume->cache)) {
+ fscache_end_cookie_access(cookie, fscache_access_unlive);
+ return false;
+ }
+ return true;
+}
+
static inline void wake_up_cookie_state(struct fscache_cookie *cookie)
{
/* Use a barrier to ensure that waiters see the state variable
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 91a4ea08ec0b..e0d8ef212e82 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -59,6 +59,9 @@ extern struct kmem_cache *fscache_cookie_jar;
extern const struct seq_operations fscache_cookies_seq_ops;
extern void fscache_print_cookie(struct fscache_cookie *cookie, char prefix);
+extern bool fscache_begin_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why);
+
static inline void fscache_see_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where)
{
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index 6cab5d99ba4c..dad85fd84f6f 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -23,6 +23,7 @@ MODULE_PARM_DESC(fscache_debug,
EXPORT_TRACEPOINT_SYMBOL(fscache_access_cache);
EXPORT_TRACEPOINT_SYMBOL(fscache_access_volume);
+EXPORT_TRACEPOINT_SYMBOL(fscache_access);
struct workqueue_struct *fscache_wq;
EXPORT_SYMBOL(fscache_wq);
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index fbbd8a2afe12..66624407ba84 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -61,6 +61,8 @@ extern struct fscache_cookie *fscache_get_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where);
extern void fscache_put_cookie(struct fscache_cookie *cookie,
enum fscache_cookie_trace where);
+extern void fscache_end_cookie_access(struct fscache_cookie *cookie,
+ enum fscache_access_trace why);
extern void fscache_set_cookie_state(struct fscache_cookie *cookie,
enum fscache_cookie_state state);
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index 4f40cfa52469..b1a962adfd16 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -279,6 +279,35 @@ TRACE_EVENT(fscache_access_volume,
__entry->n_accesses)
);
+TRACE_EVENT(fscache_access,
+ TP_PROTO(unsigned int cookie_debug_id,
+ int ref,
+ int n_accesses,
+ enum fscache_access_trace why),
+
+ TP_ARGS(cookie_debug_id, ref, n_accesses, why),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, cookie )
+ __field(int, ref )
+ __field(int, n_accesses )
+ __field(enum fscache_access_trace, why )
+ ),
+
+ TP_fast_assign(
+ __entry->cookie = cookie_debug_id;
+ __entry->ref = ref;
+ __entry->n_accesses = n_accesses;
+ __entry->why = why;
+ ),
+
+ TP_printk("c=%08x %s r=%d a=%d",
+ __entry->cookie,
+ __print_symbolic(__entry->why, fscache_access_traces),
+ __entry->ref,
+ __entry->n_accesses)
+ );
+
TRACE_EVENT(fscache_acquire,
TP_PROTO(struct fscache_cookie *cookie),
next prev parent reply other threads:[~2021-12-22 23:17 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-22 23:13 [PATCH v4 00/68] fscache, cachefiles: Rewrite David Howells
2021-12-22 23:13 ` [PATCH v4 01/68] fscache, cachefiles: Disable configuration David Howells
2021-12-22 23:13 ` [PATCH v4 02/68] cachefiles: Delete the cachefiles driver pending rewrite David Howells
2021-12-22 23:14 ` [PATCH v4 03/68] fscache: Remove the contents of the fscache driver, " David Howells
2021-12-22 23:14 ` [PATCH v4 04/68] netfs: Display the netfs inode number in the netfs_read tracepoint David Howells
2021-12-22 23:14 ` [PATCH v4 05/68] netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space David Howells
2021-12-22 23:15 ` [PATCH v4 06/68] fscache: Introduce new driver David Howells
2021-12-22 23:15 ` [PATCH v4 07/68] fscache: Implement a hash function David Howells
2021-12-22 23:15 ` [PATCH v4 08/68] fscache: Implement cache registration David Howells
2021-12-22 23:15 ` [PATCH v4 09/68] fscache: Implement volume registration David Howells
2021-12-22 23:16 ` [PATCH v4 10/68] fscache: Implement cookie registration David Howells
2021-12-22 23:16 ` [PATCH v4 11/68] fscache: Implement cache-level access helpers David Howells
2021-12-22 23:16 ` [PATCH v4 12/68] fscache: Implement volume-level " David Howells
2021-12-22 23:17 ` David Howells [this message]
2021-12-22 23:17 ` [PATCH v4 14/68] fscache: Implement functions add/remove a cache David Howells
2021-12-22 23:17 ` [PATCH v4 15/68] fscache: Provide and use cache methods to lookup/create/free a volume David Howells
2021-12-22 23:18 ` [PATCH v4 16/68] fscache: Add a function for a cache backend to note an I/O error David Howells
2021-12-22 23:18 ` [PATCH v4 17/68] fscache: Implement simple cookie state machine David Howells
2021-12-22 23:18 ` [PATCH v4 18/68] fscache: Implement cookie user counting and resource pinning David Howells
2021-12-22 23:18 ` [PATCH v4 19/68] fscache: Implement cookie invalidation David Howells
2021-12-22 23:18 ` [PATCH v4 20/68] fscache: Provide a means to begin an operation David Howells
2021-12-22 23:19 ` [PATCH v4 21/68] fscache: Count data storage objects in a cache David Howells
2021-12-22 23:19 ` [PATCH v4 22/68] fscache: Provide read/write stat counters for the cache David Howells
2021-12-22 23:19 ` [PATCH v4 23/68] fscache: Provide a function to let the netfs update its coherency data David Howells
2021-12-22 23:19 ` [PATCH v4 24/68] netfs: Pass more information on how to deal with a hole in the cache David Howells
2021-12-22 23:20 ` [PATCH v4 25/68] fscache: Implement raw I/O interface David Howells
2021-12-22 23:20 ` [PATCH v4 26/68] fscache: Implement higher-level write " David Howells
2021-12-22 23:20 ` [PATCH v4 27/68] vfs, fscache: Implement pinning of cache usage for writeback David Howells
2021-12-22 23:20 ` [PATCH v4 28/68] fscache: Provide a function to note the release of a page David Howells
2022-01-06 15:55 ` Jeff Layton
2022-01-06 16:26 ` David Howells
2021-12-22 23:21 ` [PATCH v4 29/68] fscache: Provide a function to resize a cookie David Howells
2021-12-22 23:21 ` [PATCH v4 30/68] cachefiles: Introduce rewritten driver David Howells
2021-12-22 23:21 ` [PATCH v4 31/68] cachefiles: Define structs David Howells
2021-12-22 23:22 ` [PATCH v4 32/68] cachefiles: Add some error injection support David Howells
2021-12-22 23:22 ` [PATCH v4 33/68] cachefiles: Add a couple of tracepoints for logging errors David Howells
2021-12-22 23:22 ` [PATCH v4 34/68] cachefiles: Add cache error reporting macro David Howells
2021-12-22 23:22 ` [PATCH v4 35/68] cachefiles: Add security derivation David Howells
2021-12-22 23:23 ` [PATCH v4 36/68] cachefiles: Register a miscdev and parse commands over it David Howells
2021-12-22 23:23 ` [PATCH v4 37/68] cachefiles: Provide a function to check how much space there is David Howells
2021-12-22 23:23 ` [PATCH v4 38/68] vfs, cachefiles: Mark a backing file in use with an inode flag David Howells
2022-01-06 17:04 ` Jeff Layton
2022-01-08 7:08 ` Amir Goldstein
2022-01-08 7:17 ` Matthew Wilcox
2022-01-10 7:53 ` Christoph Hellwig
2022-01-10 11:31 ` David Howells
2022-01-08 8:43 ` David Howells
2022-01-08 8:41 ` David Howells
2021-12-22 23:23 ` [PATCH v4 39/68] cachefiles: Implement a function to get/create a directory in the cache David Howells
2021-12-22 23:23 ` [PATCH v4 40/68] cachefiles: Implement cache registration and withdrawal David Howells
2022-01-06 17:17 ` Jeff Layton
2022-01-06 17:44 ` David Howells
2021-12-22 23:24 ` [PATCH v4 41/68] cachefiles: Implement volume support David Howells
2021-12-22 23:24 ` [PATCH v4 42/68] cachefiles: Add tracepoints for calls to the VFS David Howells
2021-12-22 23:24 ` [PATCH v4 43/68] cachefiles: Implement object lifecycle funcs David Howells
2021-12-22 23:24 ` [PATCH v4 44/68] cachefiles: Implement key to filename encoding David Howells
2022-01-06 17:43 ` Jeff Layton
2022-01-07 11:19 ` David Howells
2021-12-22 23:25 ` [PATCH v4 45/68] cachefiles: Implement metadata/coherency data storage in xattrs David Howells
2021-12-22 23:25 ` [PATCH v4 46/68] cachefiles: Mark a backing file in use with an inode flag David Howells
2022-01-06 18:04 ` Jeff Layton
2022-01-07 11:25 ` David Howells
2021-12-22 23:25 ` [PATCH v4 47/68] cachefiles: Implement culling daemon commands David Howells
2021-12-22 23:26 ` [PATCH v4 48/68] cachefiles: Implement backing file wrangling David Howells
2021-12-22 23:26 ` [PATCH v4 49/68] cachefiles: Implement begin and end I/O operation David Howells
2021-12-22 23:26 ` [PATCH v4 50/68] cachefiles: Implement cookie resize for truncate David Howells
2021-12-22 23:27 ` [PATCH v4 51/68] cachefiles: Implement the I/O routines David Howells
2021-12-22 23:27 ` [PATCH v4 52/68] fscache, cachefiles: Store the volume coherency data David Howells
2021-12-22 23:27 ` [PATCH v4 53/68] cachefiles: Allow cachefiles to actually function David Howells
2021-12-22 23:27 ` [PATCH v4 54/68] fscache, cachefiles: Display stats of no-space events David Howells
2021-12-22 23:27 ` [PATCH v4 55/68] fscache, cachefiles: Display stat of culling events David Howells
2021-12-22 23:28 ` [PATCH v4 56/68] afs: Convert afs to use the new fscache API David Howells
2021-12-22 23:28 ` [PATCH v4 57/68] afs: Copy local writes to the cache when writing to the server David Howells
2021-12-22 23:28 ` [PATCH v4 58/68] afs: Skip truncation on the server of data we haven't written yet David Howells
2021-12-22 23:28 ` [PATCH v4 59/68] 9p: Use fscache indexing rewrite and reenable caching David Howells
2021-12-22 23:29 ` [PATCH v4 60/68] 9p: Copy local writes to the cache when writing to the server David Howells
2021-12-22 23:29 ` [PATCH v4 61/68] nfs: Convert to new fscache volume/cookie API David Howells
2021-12-22 23:29 ` [PATCH v4 62/68] nfs: Implement cache I/O by accessing the cache directly David Howells
2021-12-22 23:29 ` [PATCH v4 63/68] cifs: Support fscache indexing rewrite (untested) David Howells
2021-12-22 23:30 ` [PATCH v4 64/68] ceph: conversion to new fscache API David Howells
2021-12-22 23:30 ` [PATCH v4 65/68] ceph: add fscache writeback support David Howells
2021-12-22 23:30 ` [PATCH v4 66/68] fscache: Rewrite documentation David Howells
2021-12-22 23:31 ` [PATCH v4 67/68] fscache: Add a tracepoint for cookie use/unuse David Howells
2021-12-22 23:31 ` [PATCH v4 68/68] 9p, afs, ceph, cifs, nfs: Use current_is_kswapd() rather than gfpflags_allow_blocking() David Howells
2022-01-04 10:50 ` [PATCH v4 00/68] fscache, cachefiles: Rewrite Jeff Layton
2022-01-04 11:27 ` David Wysochanski
2022-01-06 18:19 ` [Linux-cachefs] " Marc Dionne
2022-01-06 18:29 ` Jeff Layton
2022-01-07 21:52 ` [PATCH v4 63/68] cifs: Support fscache indexing rewrite (untested) David Howells
2022-01-09 15:27 ` Jeff Layton
2022-01-07 22:16 ` [PATCH v5 63/68] cifs: Support fscache indexing rewrite David Howells
2022-01-10 11:21 ` [PATCH v4 00/68] fscache, cachefiles: Rewrite Dominique Martinet
2022-01-12 7:20 ` [PATCH v5 63/68] cifs: Support fscache indexing rewrite David Howells
2022-01-12 21:56 ` [PATCH v6] " David Howells
2022-01-13 16:20 ` David Howells
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