From: Coly Li Date: Sat, 9 Feb 2019 04:53:11 +0000 (+0800) Subject: bcache: use (REQ_META|REQ_PRIO) to indicate bio for metadata X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=dc7292a5bcb4c878b076fca2ac3fc22f81b8f8df;p=openwrt%2Fstaging%2Fblogic.git bcache: use (REQ_META|REQ_PRIO) to indicate bio for metadata In 'commit 752f66a75aba ("bcache: use REQ_PRIO to indicate bio for metadata")' REQ_META is replaced by REQ_PRIO to indicate metadata bio. This assumption is not always correct, e.g. XFS uses REQ_META to mark metadata bio other than REQ_PRIO. This is why Nix noticed that bcache does not cache metadata for XFS after the above commit. Thanks to Dave Chinner, he explains the difference between REQ_META and REQ_PRIO from view of file system developer. Here I quote part of his explanation from mailing list, REQ_META is used for metadata. REQ_PRIO is used to communicate to the lower layers that the submitter considers this IO to be more important that non REQ_PRIO IO and so dispatch should be expedited. IOWs, if the filesystem considers metadata IO to be more important that user data IO, then it will use REQ_PRIO | REQ_META rather than just REQ_META. Then it seems bios with REQ_META or REQ_PRIO should both be cached for performance optimation, because they are all probably low I/O latency demand by upper layer (e.g. file system). So in this patch, when we want to decide whether to bypass the cache, REQ_META and REQ_PRIO are both checked. Then both metadata and high priority I/O requests will be handled properly. Reported-by: Nix Signed-off-by: Coly Li Reviewed-by: Andre Noll Tested-by: Nix Cc: stable@vger.kernel.org Cc: Dave Chinner Cc: Christoph Hellwig Signed-off-by: Jens Axboe --- diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index 15070412a32e..f101bfe8657a 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -392,10 +392,11 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio) /* * Flag for bypass if the IO is for read-ahead or background, - * unless the read-ahead request is for metadata (eg, for gfs2). + * unless the read-ahead request is for metadata + * (eg, for gfs2 or xfs). */ if (bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND) && - !(bio->bi_opf & REQ_PRIO)) + !(bio->bi_opf & (REQ_META|REQ_PRIO))) goto skip; if (bio->bi_iter.bi_sector & (c->sb.block_size - 1) || @@ -877,7 +878,7 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s, } if (!(bio->bi_opf & REQ_RAHEAD) && - !(bio->bi_opf & REQ_PRIO) && + !(bio->bi_opf & (REQ_META|REQ_PRIO)) && s->iop.c->gc_stats.in_use < CUTOFF_CACHE_READA) reada = min_t(sector_t, dc->readahead >> 9, get_capacity(bio->bi_disk) - bio_end_sector(bio));