Re: reduce memory allocation in the btrfs direct I/O path v2

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On 5/6/22 01:41, Christoph Hellwig wrote:
Hi all,

this series adds two minor improvements to iomap that allow btrfs
to avoid a memory allocation per read/write system call and another
one per submitted bio.  I also have at last two other pending uses
for the iomap functionality later on, so they are not really btrfs
specific either.

Changes since v1:
  - pass the private data direct to iomap_dio_rw instead of through the
    iocb
  - better document the bio_set in iomap_dio_ops
  - split a patch into three
  - use kcalloc to allocate the checksums

Diffstat:
  fs/btrfs/btrfs_inode.h |   25 --------
  fs/btrfs/ctree.h       |    6 -
  fs/btrfs/file.c        |    6 -
  fs/btrfs/inode.c       |  152 +++++++++++++++++++++++--------------------------
  fs/erofs/data.c        |    2
  fs/ext4/file.c         |    4 -
  fs/f2fs/file.c         |    4 -
  fs/gfs2/file.c         |    4 -
  fs/iomap/direct-io.c   |   26 ++++++--
  fs/xfs/xfs_file.c      |    6 -
  fs/zonefs/super.c      |    4 -
  include/linux/iomap.h  |   16 ++++-
  12 files changed, 123 insertions(+), 132 deletions(-)

This patch got me curious a couple of days back while I was tracing
a dio read performance issue on nvme. I am sharing the results as below.
[1]. There is no performance difference. Thx.


[1]
Before:
4971MB/s 4474GB iocounts: nvme3n1 545220968 nvme0n1 547007640 single_d2/5.18.0-rc5+_misc-next_1

After:
4968MB/s 4471GB iocounts: nvme3n1 544207371 nvme1n1 547458037 single_d2/5.18.0-rc5+_dio_cleanup_hch_1

 readstat /btrfs fio --eta=auto --output=$CMDLOG \
--name fiotest --directory=/btrfs --rw=randread \
--bs=4k --size=4G --ioengine=libaio --iodepth=16 --direct=1 \
--time_based=1 --runtime=900 --randrepeat=1 --gtod_reduce=1 \
--group_reporting=1 --numjobs=64



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