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, 8 insertions, 4 deletions

diff --git a/fs/fscache/stats.c b/fs/fscache/stats.c
index 20233fb44bfd..4c07439d1307 100644
--- a/fs/fscache/stats.c
+++ b/fs/fscache/stats.c
@@ -25,6 +25,7 @@ atomic_t fscache_n_op_requeue;
 atomic_t fscache_n_op_deferred_release;
 atomic_t fscache_n_op_release;
 atomic_t fscache_n_op_gc;
+atomic_t fscache_n_op_cancelled;
 
 atomic_t fscache_n_attr_changed;
 atomic_t fscache_n_attr_changed_ok;
@@ -36,6 +37,7 @@ atomic_t fscache_n_allocs;
 atomic_t fscache_n_allocs_ok;
 atomic_t fscache_n_allocs_wait;
 atomic_t fscache_n_allocs_nobufs;
+atomic_t fscache_n_allocs_intr;
 atomic_t fscache_n_alloc_ops;
 atomic_t fscache_n_alloc_op_waits;
 
@@ -169,11 +171,12 @@ static int fscache_stats_show(struct seq_file *m, void *v)
                    atomic_read(&fscache_n_attr_changed_nomem),
                    atomic_read(&fscache_n_attr_changed_calls));
 
-        seq_printf(m, "Allocs : n=%u ok=%u wt=%u nbf=%u\n",
+        seq_printf(m, "Allocs : n=%u ok=%u wt=%u nbf=%u int=%u\n",
                    atomic_read(&fscache_n_allocs),
                    atomic_read(&fscache_n_allocs_ok),
                    atomic_read(&fscache_n_allocs_wait),
-                   atomic_read(&fscache_n_allocs_nobufs));
+                   atomic_read(&fscache_n_allocs_nobufs),
+                   atomic_read(&fscache_n_allocs_intr));
         seq_printf(m, "Allocs : ops=%u owt=%u\n",
                    atomic_read(&fscache_n_alloc_ops),
                    atomic_read(&fscache_n_alloc_op_waits));
@@ -201,10 +204,11 @@ static int fscache_stats_show(struct seq_file *m, void *v)
                    atomic_read(&fscache_n_store_ops),
                    atomic_read(&fscache_n_store_calls));
 
-        seq_printf(m, "Ops    : pend=%u run=%u enq=%u\n",
+        seq_printf(m, "Ops    : pend=%u run=%u enq=%u can=%u\n",
                    atomic_read(&fscache_n_op_pend),
                    atomic_read(&fscache_n_op_run),
-                   atomic_read(&fscache_n_op_enqueue));
+                   atomic_read(&fscache_n_op_enqueue),
+                   atomic_read(&fscache_n_op_cancelled));
         seq_printf(m, "Ops    : dfr=%u rel=%u gc=%u\n",
                    atomic_read(&fscache_n_op_deferred_release),
                    atomic_read(&fscache_n_op_release),