bcache: remove member accessed from struct btree

The member 'accessed' of struct btree is used in bch_mca_scan() when
shrinking btree node caches. The original idea is, if b->accessed is
set, clean it and look at next btree node cache from c->btree_cache
list, and only shrink the caches whose b->accessed is cleaned. Then
only cold btree node cache will be shrunk.

But when I/O pressure is high, it is very probably that b->accessed
of a btree node cache will be set again in bch_btree_node_get()
before bch_mca_scan() selects it again. Then there is no chance for
bch_mca_scan() to shrink enough memory back to slub or slab system.

This patch removes member accessed from struct btree, then once a
btree node ache is selected, it will be immediately shunk. By this
change, bch_mca_scan() may release btree node cahce more efficiently.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 14d6c33..357535a 100644 (file)
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -754,14 +754,12 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
                b = list_first_entry(&c->btree_cache, struct btree, list);
                list_rotate_left(&c->btree_cache);
 
-               if (!b->accessed &&
-                   !mca_reap(b, 0, false)) {
+               if (!mca_reap(b, 0, false)) {
                        mca_bucket_free(b);
                        mca_data_free(b);
                        rw_unlock(true, b);
                        freed++;
-               } else
-                       b->accessed = 0;
+               }
        }
 out:
        mutex_unlock(&c->bucket_lock);
@@ -1069,7 +1067,6 @@ retry:
        BUG_ON(!b->written);
 
        b->parent = parent;
-       b->accessed = 1;
 
        for (; i <= b->keys.nsets && b->keys.set[i].size; i++) {
                prefetch(b->keys.set[i].tree);
@@ -1160,7 +1157,6 @@ retry:
                goto retry;
        }
 
-       b->accessed = 1;
        b->parent = parent;
        bch_bset_init_next(&b->keys, b->keys.set->data, bset_magic(&b->c->sb));
 

diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index 76cfd12..f4dcca4 100644 (file)
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -121,8 +121,6 @@ struct btree {
        /* Key/pointer for this btree node */
        BKEY_PADDED(key);
 
-       /* Single bit - set when accessed, cleared by shrinker */
-       unsigned long           accessed;
        unsigned long           seq;
        struct rw_semaphore     lock;
        struct cache_set        *c;