Re: [PATCH v2] md: Use optimal I/O size for last bitmap page
From: Xiao Ni <hidden>
Date: 2023-02-21 02:40:04
On Sat, Feb 18, 2023 at 2:36 AM Jonathan Derrick [off-list ref] wrote:
From: Jon Derrick <jonathan.derrick@linux.dev> If the bitmap space has enough room, size the I/O for the last bitmap page write to the optimal I/O size for the storage device. The expanded write is checked that it won't overrun the data or metadata. This change helps increase performance by preventing unnecessary device-side read-mod-writes due to non-atomic write unit sizes.
Hi Jonathan Thanks for your patch. Could you explain more about the how the optimal io size can affect the device-side read-mod-writes? Regards Xiao
quoted hunk ↗ jump to hunk
Example Intel/Solidigm P5520 Raid10, Chunk-size 64M, bitmap-size 57228 bits $ mdadm --create /dev/md0 --level=10 --raid-devices=4 /dev/nvme{0,1,2,3}n1 --assume-clean --bitmap=internal --bitmap-chunk=64M $ fio --name=test --direct=1 --filename=/dev/md0 --rw=randwrite --bs=4k --runtime=60 Without patch: write: IOPS=1676, BW=6708KiB/s (6869kB/s)(393MiB/60001msec); 0 zone resets With patch: write: IOPS=15.7k, BW=61.4MiB/s (64.4MB/s)(3683MiB/60001msec); 0 zone resets Biosnoop: Without patch: Time Process PID Device LBA Size Lat 1.410377 md0_raid10 6900 nvme0n1 W 16 4096 0.02 1.410387 md0_raid10 6900 nvme2n1 W 16 4096 0.02 1.410374 md0_raid10 6900 nvme3n1 W 16 4096 0.01 1.410381 md0_raid10 6900 nvme1n1 W 16 4096 0.02 1.410411 md0_raid10 6900 nvme1n1 W 115346512 4096 0.01 1.410418 md0_raid10 6900 nvme0n1 W 115346512 4096 0.02 1.410915 md0_raid10 6900 nvme2n1 W 24 3584 0.43 1.410935 md0_raid10 6900 nvme3n1 W 24 3584 0.45 1.411124 md0_raid10 6900 nvme1n1 W 24 3584 0.64 1.411147 md0_raid10 6900 nvme0n1 W 24 3584 0.66 1.411176 md0_raid10 6900 nvme3n1 W 2019022184 4096 0.01 1.411189 md0_raid10 6900 nvme2n1 W 2019022184 4096 0.02 With patch: Time Process PID Device LBA Size Lat 5.747193 md0_raid10 727 nvme0n1 W 16 4096 0.01 5.747192 md0_raid10 727 nvme1n1 W 16 4096 0.02 5.747195 md0_raid10 727 nvme3n1 W 16 4096 0.01 5.747202 md0_raid10 727 nvme2n1 W 16 4096 0.02 5.747229 md0_raid10 727 nvme3n1 W 1196223704 4096 0.02 5.747224 md0_raid10 727 nvme0n1 W 1196223704 4096 0.01 5.747279 md0_raid10 727 nvme0n1 W 24 4096 0.01 5.747279 md0_raid10 727 nvme1n1 W 24 4096 0.02 5.747284 md0_raid10 727 nvme3n1 W 24 4096 0.02 5.747291 md0_raid10 727 nvme2n1 W 24 4096 0.02 5.747314 md0_raid10 727 nvme2n1 W 2234636712 4096 0.01 5.747317 md0_raid10 727 nvme1n1 W 2234636712 4096 0.02 Signed-off-by: Jon Derrick <jonathan.derrick@linux.dev> --- v1->v2: Add more information to commit message drivers/md/md-bitmap.c | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-)diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c index e7cc6ba1b657..569297ea9b99 100644 --- a/drivers/md/md-bitmap.c +++ b/drivers/md/md-bitmap.c@@ -220,6 +220,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait) rdev = NULL; while ((rdev = next_active_rdev(rdev, mddev)) != NULL) { int size = PAGE_SIZE; + int optimal_size = PAGE_SIZE; loff_t offset = mddev->bitmap_info.offset; bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;@@ -228,9 +229,14 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait) int last_page_size = store->bytes & (PAGE_SIZE-1); if (last_page_size == 0) last_page_size = PAGE_SIZE; - size = roundup(last_page_size, - bdev_logical_block_size(bdev)); + size = roundup(last_page_size, bdev_logical_block_size(bdev)); + if (bdev_io_opt(bdev) > bdev_logical_block_size(bdev)) + optimal_size = roundup(last_page_size, bdev_io_opt(bdev)); + else + optimal_size = size; } + + /* Just make sure we aren't corrupting data or * metadata */@@ -246,9 +252,11 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait) goto bad_alignment; } else if (offset < 0) { /* DATA BITMAP METADATA */ - if (offset - + (long)(page->index * (PAGE_SIZE/512)) - + size/512 > 0) + loff_t off = offset + (long)(page->index * (PAGE_SIZE/512)); + if (size != optimal_size && + off + optimal_size/512 <= 0) + size = optimal_size; + else if (off + size/512 > 0) /* bitmap runs in to metadata */ goto bad_alignment; if (rdev->data_offset + mddev->dev_sectors@@ -257,10 +265,11 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait) goto bad_alignment; } else if (rdev->sb_start < rdev->data_offset) { /* METADATA BITMAP DATA */ - if (rdev->sb_start - + offset - + page->index*(PAGE_SIZE/512) + size/512 - > rdev->data_offset) + loff_t off = rdev->sb_start + offset + page->index*(PAGE_SIZE/512); + if (size != optimal_size && + off + optimal_size/512 <= rdev->data_offset) + size = optimal_size; + else if (off + size/512 > rdev->data_offset) /* bitmap runs in to data */ goto bad_alignment; } else { --2.27.0