On 2016/9/3 2:36, Jaegeuk Kim wrote: > On Fri, Sep 02, 2016 at 03:33:33PM +0800, Chao Yu wrote: >> Hi Jaegeuk, >> >> On 2016/8/27 8:53, Jaegeuk Kim wrote: >>> This can avoid bio splits due to different op_flags. >> >> I thought about this, but I think this is not a good idea to increase merging >> ratio of pages in bio. It breaks the rule of SYNC/ASYNC IO defined by system >> which indicate degree of IO emergency, finally, some/more non-emergent IO >> will >> treated as emergent one by IO scheduler, it will interrupt SYNC IOs in block >> layer, more seriously, it may make real SYNC IO starvation. > > I understand your concern. > Originally, I tried to avoid breaking a big WRITE_SYNC by a small number of
Hmm.. I'm worry about the opposite case: user triggers small WRITE_SYNC IO periodically, meanwhile there are big number of WRITE, with our new approach, actually we will increase the number of synchronous WRITE IO obviously because we will mix ASYNC/SYNC WRITE into bio cache intensively more than before since we drop writepages mutexlock. So I'm afread the result is that it will mislead scheduling of block layer. > WRITE. And, I thought new WRITE can be piggybacked into previous WRITE_SYNC. > > IMO, this happens very occassionally since previous pending bio should be > WRITE_SYNC while a new request is WRITE. Even if this happens, the piggybacked > size would not exceed over bio's max pages. > If lots of WRITE come, we won't change at all. I thinks this is related to writeback / blocklayer / cgroup subsystem which use this tag frequently, maybe we should Cc their's mailing list for more opinion... What's your opinion? :) thanks, > > Thanks, > >> >> Thanks, >> >>> >>> Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org> >>> --- >>> fs/f2fs/data.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >>> index 7c8e219..c7c2022 100644 >>> --- a/fs/f2fs/data.c >>> +++ b/fs/f2fs/data.c >>> @@ -267,6 +267,11 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio) >>> >>> down_write(&io->io_rwsem); >>> >>> + /* WRITE can be merged into previous WRITE_SYNC */ >>> + if (io->bio && io->last_block_in_bio == fio->new_blkaddr - 1 && >>> + io->fio.op == fio->op && io->fio.op_flags == WRITE_SYNC) >>> + fio->op_flags = WRITE_SYNC; >>> + >>> if (io->bio && (io->last_block_in_bio != fio->new_blkaddr - 1 || >>> (io->fio.op != fio->op || io->fio.op_flags != fio->op_flags))) >>> __submit_merged_bio(io); >>> > > ------------------------------------------------------------------------------ > _______________________________________________ > Linux-f2fs-devel mailing list > linux-f2fs-de...@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel >
