From 369200446564f04b5cd14596d69e17880be7d926 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Thu, 2 Jun 2022 15:51:18 +0800 Subject: [PATCH] btrfs: raid56: avoid double for loop inside finish_rmw() We can easily calculate the stripe number and sector number inside the stripe. Thus there is not much need for a double for loop. For the only case we want to skip the whole stripe, we can manually increase @total_sector_nr. This is not a recommended behavior, thus every time the iterator gets modified there will be a comment along with an ASSERT() for it. Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/raid56.c | 97 +++++++++++++++++++++++++++++++------------------------ 1 file changed, 55 insertions(+), 42 deletions(-) diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c index 3c58869..c63845c 100644 --- a/fs/btrfs/raid56.c +++ b/fs/btrfs/raid56.c @@ -1182,7 +1182,10 @@ static noinline void finish_rmw(struct btrfs_raid_bio *rbio) const u32 sectorsize = bioc->fs_info->sectorsize; void **pointers = rbio->finish_pointers; int nr_data = rbio->nr_data; + /* The total sector number inside the full stripe. */ + int total_sector_nr; int stripe; + /* Sector number inside a stripe. */ int sectornr; bool has_qstripe; struct bio_list bio_list; @@ -1267,63 +1270,73 @@ static noinline void finish_rmw(struct btrfs_raid_bio *rbio) } /* - * time to start writing. Make bios for everything from the - * higher layers (the bio_list in our rbio) and our p/q. Ignore - * everything else. + * Start writing. Make bios for everything from the higher layers (the + * bio_list in our rbio) and our P/Q. Ignore everything else. */ - for (stripe = 0; stripe < rbio->real_stripes; stripe++) { - for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) { - struct sector_ptr *sector; + for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors; + total_sector_nr++) { + struct sector_ptr *sector; - /* This vertical stripe has no data, skip it. */ - if (!test_bit(sectornr, &rbio->dbitmap)) - continue; + stripe = total_sector_nr / rbio->stripe_nsectors; + sectornr = total_sector_nr % rbio->stripe_nsectors; - if (stripe < rbio->nr_data) { - sector = sector_in_rbio(rbio, stripe, sectornr, 1); - if (!sector) - continue; - } else { - sector = rbio_stripe_sector(rbio, stripe, sectornr); - } + /* This vertical stripe has no data, skip it. */ + if (!test_bit(sectornr, &rbio->dbitmap)) + continue; - ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe, - sectornr, rbio->stripe_len, - REQ_OP_WRITE); - if (ret) - goto cleanup; + if (stripe < rbio->nr_data) { + sector = sector_in_rbio(rbio, stripe, sectornr, 1); + if (!sector) + continue; + } else { + sector = rbio_stripe_sector(rbio, stripe, sectornr); } + + ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe, + sectornr, rbio->stripe_len, + REQ_OP_WRITE); + if (ret) + goto cleanup; } if (likely(!bioc->num_tgtdevs)) goto write_data; - for (stripe = 0; stripe < rbio->real_stripes; stripe++) { - if (!bioc->tgtdev_map[stripe]) - continue; + for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors; + total_sector_nr++) { + struct sector_ptr *sector; - for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) { - struct sector_ptr *sector; + stripe = total_sector_nr / rbio->stripe_nsectors; + sectornr = total_sector_nr % rbio->stripe_nsectors; - /* This vertical stripe has no data, skip it. */ - if (!test_bit(sectornr, &rbio->dbitmap)) - continue; + if (!bioc->tgtdev_map[stripe]) { + /* + * We can skip the whole stripe completely, note + * total_sector_nr will be increased by one anyway. + */ + ASSERT(sectornr == 0); + total_sector_nr += rbio->stripe_nsectors - 1; + continue; + } - if (stripe < rbio->nr_data) { - sector = sector_in_rbio(rbio, stripe, sectornr, 1); - if (!sector) - continue; - } else { - sector = rbio_stripe_sector(rbio, stripe, sectornr); - } + /* This vertical stripe has no data, skip it. */ + if (!test_bit(sectornr, &rbio->dbitmap)) + continue; - ret = rbio_add_io_sector(rbio, &bio_list, sector, - rbio->bioc->tgtdev_map[stripe], - sectornr, rbio->stripe_len, - REQ_OP_WRITE); - if (ret) - goto cleanup; + if (stripe < rbio->nr_data) { + sector = sector_in_rbio(rbio, stripe, sectornr, 1); + if (!sector) + continue; + } else { + sector = rbio_stripe_sector(rbio, stripe, sectornr); } + + ret = rbio_add_io_sector(rbio, &bio_list, sector, + rbio->bioc->tgtdev_map[stripe], + sectornr, rbio->stripe_len, + REQ_OP_WRITE); + if (ret) + goto cleanup; } write_data: -- 2.7.4