[v4,15/16] bcache: avoid extra memory allocation from mempool c->fill_iter
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Message ID 20200717112236.44761-16-colyli@suse.de
State New
Headers show
  • bcache: extend bucket size to 32bit width
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Commit Message

Coly Li July 17, 2020, 11:22 a.m. UTC
Mempool c->fill_iter is used to allocate memory for struct btree_iter in
bch_btree_node_read_done() to iterate all keys of a read-in btree node.

The allocation size is defined in bch_cache_set_alloc() by,
  mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size))
where iter_size is defined by a calculation,
  (sb->bucket_size / sb->block_size + 1) * sizeof(struct btree_iter_set)

For 16bit width bucket_size the calculation is OK, but now the bucket
size is extended to 32bit, the bucket size can be 2GB. By the above
calculation, iter_size can be 2048 pages (order 11 is still accepted by
buddy allocator).

But the actual size holds the bkeys in meta data bucket is limited to
meta_bucket_pages() already, which is 16MB. By the above calculation,
if replace sb->bucket_size by meta_bucket_pages() * PAGE_SECTORS, the
result is 16 pages. This is the size large enough for the mempool
allocation to struct btree_iter.

Therefore in worst case every time mempool c->fill_iter allocates, at
most 4080 pages are wasted and won't be used. Therefore this patch uses
meta_bucket_pages() * PAGE_SECTORS to calculate the iter size in
bch_cache_set_alloc(), to avoid extra memory allocation from mempool

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
 drivers/md/bcache/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index b7ef11da026c..d86b31722b41 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1908,7 +1908,7 @@  struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
-	iter_size = (sb->bucket_size / sb->block_size + 1) *
+	iter_size = ((meta_bucket_pages(sb) * PAGE_SECTORS) / sb->block_size + 1) *
 		sizeof(struct btree_iter_set);
 	c->devices = kcalloc(c->nr_uuids, sizeof(void *), GFP_KERNEL);