mm: new shrinker API

The current shrinker callout API uses an a single shrinker call for
multiple functions.  To determine the function, a special magical value is
passed in a parameter to change the behaviour.  This complicates the
implementation and return value specification for the different
behaviours.

Separate the two different behaviours into separate operations, one to
return a count of freeable objects in the cache, and another to scan a
certain number of objects in the cache for freeing.  In defining these new
operations, ensure the return values and resultant behaviours are clearly
defined and documented.

Modify shrink_slab() to use the new API and implement the callouts for all
the existing shrinkers.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Glauber Costa <glommer@parallels.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Rientjes <rientjes@google.com>
Cc: Gleb Natapov <gleb@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: J. Bruce Fields <bfields@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 40 insertions, 20 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2cff0d491c6d..4d4e859b4b9c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -205,19 +205,24 @@ static inline int do_shrinker_shrink(struct shrinker *shrinker,
  *
  * Returns the number of slab objects which we shrunk.
  */
-unsigned long shrink_slab(struct shrink_control *shrink,
+unsigned long shrink_slab(struct shrink_control *shrinkctl,
                           unsigned long nr_pages_scanned,
                           unsigned long lru_pages)
 {
         struct shrinker *shrinker;
-        unsigned long ret = 0;
+        unsigned long freed = 0;
 
         if (nr_pages_scanned == 0)
                 nr_pages_scanned = SWAP_CLUSTER_MAX;
 
         if (!down_read_trylock(&shrinker_rwsem)) {
-                /* Assume we'll be able to shrink next time */
-                ret = 1;
+                /*
+                 * If we would return 0, our callers would understand that we
+                 * have nothing else to shrink and give up trying. By returning
+                 * 1 we keep it going and assume we'll be able to shrink next
+                 * time.
+                 */
+                freed = 1;
                 goto out;
         }
 
@@ -225,14 +230,16 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                 unsigned long long delta;
                 long total_scan;
                 long max_pass;
-                int shrink_ret = 0;
                 long nr;
                 long new_nr;
                 long batch_size = shrinker->batch ? shrinker->batch
                                                   : SHRINK_BATCH;
 
-                max_pass = do_shrinker_shrink(shrinker, shrink, 0);
-                if (max_pass <= 0)
+                if (shrinker->count_objects)
+                        max_pass = shrinker->count_objects(shrinker, shrinkctl);
+                else
+                        max_pass = do_shrinker_shrink(shrinker, shrinkctl, 0);
+                if (max_pass == 0)
                         continue;
 
                 /*
@@ -248,8 +255,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                 do_div(delta, lru_pages + 1);
                 total_scan += delta;
                 if (total_scan < 0) {
-                        printk(KERN_ERR "shrink_slab: %pF negative objects to "
-                               "delete nr=%ld\n",
+                        printk(KERN_ERR
+                        "shrink_slab: %pF negative objects to delete nr=%ld\n",
                                shrinker->shrink, total_scan);
                         total_scan = max_pass;
                 }
@@ -277,20 +284,33 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                 if (total_scan > max_pass * 2)
                         total_scan = max_pass * 2;
 
-                trace_mm_shrink_slab_start(shrinker, shrink, nr,
+                trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
                                         nr_pages_scanned, lru_pages,
                                         max_pass, delta, total_scan);
 
                 while (total_scan >= batch_size) {
-                        int nr_before;
 
-                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
-                        shrink_ret = do_shrinker_shrink(shrinker, shrink,
-                                                        batch_size);
-                        if (shrink_ret == -1)
-                                break;
-                        if (shrink_ret < nr_before)
-                                ret += nr_before - shrink_ret;
+                        if (shrinker->scan_objects) {
+                                unsigned long ret;
+                                shrinkctl->nr_to_scan = batch_size;
+                                ret = shrinker->scan_objects(shrinker, shrinkctl);
+
+                                if (ret == SHRINK_STOP)
+                                        break;
+                                freed += ret;
+                        } else {
+                                int nr_before;
+                                long ret;
+
+                                nr_before = do_shrinker_shrink(shrinker, shrinkctl, 0);
+                                ret = do_shrinker_shrink(shrinker, shrinkctl,
+                                                                batch_size);
+                                if (ret == -1)
+                                        break;
+                                if (ret < nr_before)
+                                        freed += nr_before - ret;
+                        }
+
                         count_vm_events(SLABS_SCANNED, batch_size);
                         total_scan -= batch_size;
 
@@ -308,12 +328,12 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                 else
                         new_nr = atomic_long_read(&shrinker->nr_in_batch);
 
-                trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
+                trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr);
         }
         up_read(&shrinker_rwsem);
 out:
         cond_resched();
-        return ret;
+        return freed;
 }
 
 static inline int is_page_cache_freeable(struct page *page)