FS-Cache: Permit cache retrieval ops to be interrupted in the initial wait phase

Permit the operations to retrieve data from the cache or to allocate space in
the cache for future writes to be interrupted whilst they're waiting for
permission for the operation to proceed.  Typically this wait occurs whilst the
cache object is being looked up on disk in the background.

If an interruption occurs, and the operation has not yet been given the
go-ahead to run, the operation is dequeued and cancelled, and control returns
to the read operation of the netfs routine with none of the requested pages
having been read or in any way marked as known by the cache.

This means that the initial wait is done interruptibly rather than
uninterruptibly.

In addition, extra stats values are made available to show the number of ops
cancelled and the number of cache space allocations interrupted.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/filesystems/caching/fscache.txt b/Documentation/filesystems/caching/fscache.txt
index b6c32c080ab1..0a77868f4977 100644
--- a/Documentation/filesystems/caching/fscache.txt
+++ b/Documentation/filesystems/caching/fscache.txt
@@ -250,6 +250,7 @@ proc files.
                 ok=N    Number of successful alloc reqs
                 wt=N    Number of alloc reqs that waited on lookup completion
                 nbf=N   Number of alloc reqs rejected -ENOBUFS
+                int=N   Number of alloc reqs aborted -ERESTARTSYS
                 ops=N   Number of alloc reqs submitted
                 owt=N   Number of alloc reqs waited for CPU time
         Retrvls n=N     Number of retrieval (read) requests seen
@@ -271,6 +272,7 @@ proc files.
         Ops     pend=N  Number of times async ops added to pending queues
                 run=N   Number of times async ops given CPU time
                 enq=N   Number of times async ops queued for processing
+                can=N   Number of async ops cancelled
                 dfr=N   Number of async ops queued for deferred release
                 rel=N   Number of async ops released
                 gc=N    Number of deferred-release async ops garbage collected