a7733fb632
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cookie is being withdrawn and we're waiting for it to quiesce - at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
Link: https://lore.kernel.org/r/164021503063.640689.8870918985269528670.stgit@warthog.procyon.org.uk/ # v4
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| linux | ||
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