bcache: handle btree node memory allocation properly for bucket size > 8MB

Currently the bcache internal btree node occupies a whole bucket. When
loading the btree node from cache device into memory, mca_data_alloc()
will call bch_btree_keys_alloc() to allocate memory for the whole bucket
size, ilog2(b->c->btree_pages) is send to bch_btree_keys_alloc() as the
parameter 'page_order'.

c->btree_pages is set as bucket_pages() in bch_cache_set_alloc(), for
bucket size > 8MB, ilog2(b->c->btree_pages) is 12 for 4KB page size. By
default the maximum page order __get_free_pages() accepts is MAX_ORDER
(11), in this condition bch_btree_keys_alloc() will always fail.

Because of other over-page-order allocation failure fails the cache
device registration, such btree node allocation failure wasn't observed
during runtime. After other blocking page allocation failures for bucket
size > 8MB, this btree node allocation issue may trigger potentical risk
e.g. infinite dead-loop to retry btree node allocation after failure.

This patch fixes the potential problem by setting c->btree_pages to
meta_bucket_pages() in bch_cache_set_alloc(). In the condition that
bucket size > 8MB, meta_bucket_pages() will always return a number which
won't exceed the maximum page order of the buddy allocator.

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

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index b5ad481..e4f05c4 100644 (file)
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1875,7 +1875,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
        c->nr_uuids             = meta_bucket_bytes(&c->sb) / sizeof(struct uuid_entry);
        c->devices_max_used     = 0;
        atomic_set(&c->attached_dev_nr, 0);
-       c->btree_pages          = bucket_pages(c);
+       c->btree_pages          = meta_bucket_pages(&c->sb);
        if (c->btree_pages > BTREE_MAX_PAGES)
                c->btree_pages = max_t(int, c->btree_pages / 4,
                                       BTREE_MAX_PAGES);