vmscan: add customisable shrinker batch size

For shrinkers that have their own cond_resched* calls, having
shrink_slab break the work down into small batches is not
paticularly efficient. Add a custom batchsize field to the struct
shrinker so that shrinkers can use a larger batch size if they
desire.

A value of zero (uninitialised) means "use the default", so
behaviour is unchanged by this patch.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9670f71..9b9777a 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1150,6 +1150,7 @@ struct shrink_control {
 struct shrinker {
        int (*shrink)(struct shrinker *, struct shrink_control *sc);
        int seeks;      /* seeks to recreate an obj */
+       long batch;     /* reclaim batch size, 0 = default */
 
        /* These are for internal use */
        struct list_head list;

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3874224..febbc04 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -253,6 +253,8 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                int shrink_ret = 0;
                long nr;
                long new_nr;
+               long batch_size = shrinker->batch ? shrinker->batch
+                                                 : SHRINK_BATCH;
 
                /*
                 * copy the current shrinker scan count into a local variable
@@ -303,19 +305,18 @@ unsigned long shrink_slab(struct shrink_control *shrink,
                                        nr_pages_scanned, lru_pages,
                                        max_pass, delta, total_scan);
 
-               while (total_scan >= SHRINK_BATCH) {
-                       long this_scan = SHRINK_BATCH;
+               while (total_scan >= batch_size) {
                        int nr_before;
 
                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
                        shrink_ret = do_shrinker_shrink(shrinker, shrink,
-                                                       this_scan);
+                                                       batch_size);
                        if (shrink_ret == -1)
                                break;
                        if (shrink_ret < nr_before)
                                ret += nr_before - shrink_ret;
-                       count_vm_events(SLABS_SCANNED, this_scan);
-                       total_scan -= this_scan;
+                       count_vm_events(SLABS_SCANNED, batch_size);
+                       total_scan -= batch_size;
 
                        cond_resched();
                }