diff options
| -rw-r--r-- | fs/fscache/cookie.c | 98 | ||||
| -rw-r--r-- | fs/fscache/internal.h | 3 | ||||
| -rw-r--r-- | fs/fscache/main.c | 1 | ||||
| -rw-r--r-- | include/linux/fscache-cache.h | 2 | ||||
| -rw-r--r-- | include/trace/events/fscache.h | 29 |
5 files changed, 133 insertions, 0 deletions
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), |