Hello, Please find the RFC patchset which adds support for iomap subpage dirty state tracking which improves write performance and should reduce the write amplification on platforms with smaller filesystem blocksize compared to pagesize. E.g. On Power with 64k default pagesize and with 4k XFS filesystem blocksize. I have done some minimal fsstress and fstests testing using this patchset and haven't noticed any issues as such. Posting this RFC to get some initial comments/thoughts on the patch. I will run full fstests with XFS if this RFC looks good. >From review perspective, it will be helpful if one can also review the error handling path. I wasn't sure on whether we need to clear the dirty state bitmap of blocks within a folio or not in iomap_writepage_map(). I don't clear that, since AFAIU, the error in that function is due to failed ->map_blocks() function which has nothing to do with tracking subpage dirty state of a block within folio. But please let me know your thoughts on this or other error handling path. Performance results ====================== 1. Performance testing of below fio workload reveals ~16x performance improvement on nvme with XFS (4k blocksize) on Power (64K pagesize) FIO reported write bw scores, improved from ~28 MBps to ~452 MBps. <test_randwrite.fio> [global] ioengine=psync rw=randwrite overwrite=1 pre_read=1 direct=0 bs=4k size=1G dir=./ numjobs=8 fdatasync=1 runtime=60 iodepth=64 group_reporting=1 [fio-run] 2. Also our internal performance team reported that this patch improves there database workload performance by around ~83% (with XFS on Power) Note: I did come across an older RFC around the same logic to track subpage dirty tracking here [1]. But it seems no one pursued it after iomap received folio changes update. [1]: https://lore.kernel.org/linux-xfs/20200821123306.1658495-1-yukuai3@xxxxxxxxxx/#t Ritesh Harjani (IBM) (2): iomap: Change uptodate variable name to state iomap: Support subpage size dirty tracking to improve write performance fs/iomap/buffered-io.c | 79 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 64 insertions(+), 15 deletions(-) -- 2.37.3
