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fscache: Implement cache-level access helpers

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Add a pair of functions to pin/unpin a cache that we're wanting to do a
high-level access to (such as creating or removing a volume):

	bool fscache_begin_cache_access(struct fscache_cache *cache,
					enum fscache_access_trace why);
	void fscache_end_cache_access(struct fscache_cache *cache,
				      enum fscache_access_trace why);

The way the access gate works/will work is:

 (1) If the cache tests as not live (state is not FSCACHE_CACHE_IS_ACTIVE),
     then we return false to indicate access was not permitted.

 (2) If the cache tests as live, then we increment the n_accesses count and
     then recheck the liveness, ending the access if it ceased to be live.

 (3) When we end the access, we decrement n_accesses and wake up the any
     waiters if it reaches 0.

 (4) Whilst the cache is caching, n_accesses is kept artificially
     incremented to prevent wakeups from happening.

 (5) When the cache is taken offline, the state is changed to prevent new
     accesses, n_accesses is decremented and we wait for n_accesses to
     become 0.

Note that some of this is implemented in a later patch.

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/163819593239.215744.7537428720603638088.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/163906893368.143852.14164004598465617981.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/163967093977.1823006.6967886507023056409.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021499995.640689.18286203753480287850.stgit@warthog.procyon.org.uk/ # v4
This commit is contained in:
David Howells
2021-10-20 15:00:26 +01:00
parent 7f3283aba3
commit 23e12e285a
4 changed files with 107 additions and 0 deletions
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41
include/trace/events/fscache.h
View File

@@ -62,6 +62,12 @@ enum fscache_cookie_trace {
fscache_cookie_see_work,
};
enum fscache_access_trace {
fscache_access_cache_pin,
fscache_access_cache_unpin,
fscache_access_unlive,
};
#endif
/*
@@ -107,6 +113,11 @@ enum fscache_cookie_trace {
EM(fscache_cookie_see_withdraw, "- x-wth") \
E_(fscache_cookie_see_work, "- work ")
#define fscache_access_traces \
EM(fscache_access_cache_pin, "PIN cache ") \
EM(fscache_access_cache_unpin, "UNPIN cache ") \
E_(fscache_access_unlive, "END unlive ")
/*
* Export enum symbols via userspace.
*/
@@ -118,6 +129,7 @@ enum fscache_cookie_trace {
fscache_cache_traces;
fscache_volume_traces;
fscache_cookie_traces;
fscache_access_traces;
/*
* Now redefine the EM() and E_() macros to map the enums to the strings that
@@ -204,6 +216,35 @@ TRACE_EVENT(fscache_cookie,
__entry->ref)
);
TRACE_EVENT(fscache_access_cache,
TP_PROTO(unsigned int cache_debug_id,
int ref,
int n_accesses,
enum fscache_access_trace why),
TP_ARGS(cache_debug_id, ref, n_accesses, why),
TP_STRUCT__entry(
__field(unsigned int, cache )
__field(int, ref )
__field(int, n_accesses )
__field(enum fscache_access_trace, why )
),
TP_fast_assign(
__entry->cache = cache_debug_id;
__entry->ref = ref;
__entry->n_accesses = n_accesses;
__entry->why = why;
),
TP_printk("C=%08x %s r=%d a=%d",
__entry->cache,
__print_symbolic(__entry->why, fscache_access_traces),
__entry->ref,
__entry->n_accesses)
);
TRACE_EVENT(fscache_acquire,
TP_PROTO(struct fscache_cookie *cookie),