On Fri, May 18, 2018 at 06:47:56PM +0200, Christoph Hellwig wrote:
> Hi all,
>
> this series adds support for buffered I/O without buffer heads to
> the iomap and XFS code.
>
> For now this series only contains support for block size == PAGE_SIZE,
> with the 4k support split into a separate series.
>
>
> A git tree is available at:
>
> git://git.infradead.org/users/hch/xfs.git xfs-iomap-read.2
>
> Gitweb:
>
>
> http://git.infradead.org/users/hch/xfs.git/shortlog/refs/heads/xfs-iomap-read.2
Hmm, so I pulled this and ran my trivial stupid benchmark on for-next.
It's a stupid VM with a 2G of RAM and a 12GB virtio-scsi disk backed by
tmpfs:
# mkfs.xfs -f -m rmapbt=0,reflink=1 /dev/sda
meta-data=/dev/sda isize=512 agcount=4, agsize=823296
blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1,
rmapbt=1
= reflink=1
data = bsize=4096 blocks=3293184, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=3693, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
# mount /dev/sda /mnt
# xfs_io -f -c 'pwrite -W -S 0x64 -b 83886080 0 734003200' /mnt/a
wrote 734003200/734003200 bytes at offset 0
700 MiB, 9 ops; 0:00:01.06 (655.500 MiB/sec and 8.4279 ops/sec)
# cp --reflink=always /mnt/a /mnt/b
# xfs_io -f -c 'pwrite -W -S 0x65 -b 83886080 0 734003200' /mnt/b
wrote 734003200/734003200 bytes at offset 0
700 MiB, 9 ops; 0.9620 sec (727.615 MiB/sec and 9.3551 ops/sec)
Then I applied your series (not including the blocksize < pagesize
series) and saw this big regression:
# mkfs.xfs -f -m rmapbt=0,reflink=1 /dev/sda
meta-data=/dev/sda isize=512 agcount=4, agsize=823296
blks
= sectsz=512 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=1,
rmapbt=1
= reflink=1
data = bsize=4096 blocks=3293184, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0, ftype=1
log =internal log bsize=4096 blocks=3693, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
# mount /dev/sda /mnt
# xfs_io -f -c 'pwrite -W -S 0x64 -b 83886080 0 734003200' /mnt/a
wrote 734003200/734003200 bytes at offset 0
700 MiB, 9 ops; 0:00:08.04 (87.031 MiB/sec and 1.1190 ops/sec)
# cp --reflink=always /mnt/a /mnt/b
# xfs_io -f -c 'pwrite -W -S 0x65 -b 83886080 0 734003200' /mnt/b
wrote 734003200/734003200 bytes at offset 0
700 MiB, 9 ops; 0:00:21.61 (32.389 MiB/sec and 0.4164 ops/sec)
I'll see if I can spot the problem while I read through the v2 code...
--D
>
> Changes since v1:
> - fix the iomap_readpages error handling
> - use unsigned file offsets in a few places to avoid arithmetic overflows
> - allocate a iomap_page in iomap_page_mkwrite to fix generic/095
> - improve a few comments
> - add more asserts
> - warn about truncated block numbers from ->bmap
> - new patch to change the __do_page_cache_readahead return value to
> unsigned int
> - remove an incorrectly added empty line
> - make inline data an explicit iomap type instead of a flag
> - add a IOMAP_F_BUFFER_HEAD flag to force use of buffers heads for gfs2,
> and keep the basic buffer head infrastructure around for now.
