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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.
The drive this was tested against has higher latencies when there are
sub-4k writes due to device-side read-mod-writes of its atomic 4k write
unit. This change helps increase performance by sizing the last bitmap
page I/O for the device's preferred write unit, if it is given.
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
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jon Derrick <jonathan.derrick@linux.dev>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230224183323.638-4-jonathan.derrick@linux.dev
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.