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Message-ID: <20160712170828.GB14203@jaegeuk>
Date: Tue, 12 Jul 2016 10:08:28 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, chen.chun.yen@...wei.com,
hebiao6@...wei.com
Subject: Re: [f2fs-dev] [PATCH 3/7] f2fs: drop any block plugging
Hi Chao,
On Tue, Jul 12, 2016 at 09:38:11AM +0800, Chao Yu wrote:
> On 2016/7/10 0:32, Jaegeuk Kim wrote:
> > On Sat, Jul 09, 2016 at 10:28:49AM +0800, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2016/6/9 1:24, Jaegeuk Kim wrote:
> >>> In f2fs, we don't need to keep block plugging for NODE and DATA writes, since
> >>> we already merged bios as much as possible.
> >>
> >> IMO, we can not remove block plug, this is because there are still many
> >> conditions which stops us merging r/w IOs into one bio as we expect,
> >> theoretically, block plug can hold bios as much as possible, then submitting
> >> them into queue in batch, it will reduce racing of grabbing queue->lock during
> >> bio submitting, if we drop them, when syncing nodes or flushing datas, we will
> >> suffer more lock racing.
> >>
> >> Or there are something I am missing, do you suffer any performance issue on
> >> block plug?
> >
> > In the latest patch, I've turned off plugging forcefully, only if the underlying
> > device is SMR drive.
>
> Got it.
>
> > And, still I removed other block plugging, since I couldn't see any performance
> > regression.
>
> I suspect that in low-end machine with single-queue which is used in block
> layer, we will suffer regression.
>
> > Even in some workloads, I could have seen some inverted IOs due to
> > race condition between plugged and unplugged IOs.
>
> For data path, what about enabling block plug for IPU/SSR ?
Not sure. IPU and SSR will produce small (likely random) writes.
What I'm seeing here is that we already try to merge bios as much as possible.
Thus, I'm in doubt why we need to wait for merging them by block layer.
If possible, could you check this in android?
Thanks,
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> >>> ---
> >>> fs/f2fs/checkpoint.c | 4 ----
> >>> fs/f2fs/data.c | 17 ++++++++++-------
> >>> fs/f2fs/gc.c | 5 -----
> >>> fs/f2fs/segment.c | 7 +------
> >>> 4 files changed, 11 insertions(+), 22 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> >>> index 5ddd15c..4179c7b 100644
> >>> --- a/fs/f2fs/checkpoint.c
> >>> +++ b/fs/f2fs/checkpoint.c
> >>> @@ -897,11 +897,8 @@ static int block_operations(struct f2fs_sb_info *sbi)
> >>> .nr_to_write = LONG_MAX,
> >>> .for_reclaim = 0,
> >>> };
> >>> - struct blk_plug plug;
> >>> int err = 0;
> >>>
> >>> - blk_start_plug(&plug);
> >>> -
> >>> retry_flush_dents:
> >>> f2fs_lock_all(sbi);
> >>> /* write all the dirty dentry pages */
> >>> @@ -938,7 +935,6 @@ retry_flush_nodes:
> >>> goto retry_flush_nodes;
> >>> }
> >>> out:
> >>> - blk_finish_plug(&plug);
> >>> return err;
> >>> }
> >>>
> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >>> index 30dc448..5f655d0 100644
> >>> --- a/fs/f2fs/data.c
> >>> +++ b/fs/f2fs/data.c
> >>> @@ -98,10 +98,13 @@ static struct bio *__bio_alloc(struct f2fs_sb_info *sbi, block_t blk_addr,
> >>> }
> >>>
> >>> static inline void __submit_bio(struct f2fs_sb_info *sbi, int rw,
> >>> - struct bio *bio)
> >>> + struct bio *bio, enum page_type type)
> >>> {
> >>> - if (!is_read_io(rw))
> >>> + if (!is_read_io(rw)) {
> >>> atomic_inc(&sbi->nr_wb_bios);
> >>> + if (current->plug && (type == DATA || type == NODE))
> >>> + blk_finish_plug(current->plug);
> >>> + }
> >>> submit_bio(rw, bio);
> >>> }
> >>>
> >>> @@ -117,7 +120,7 @@ static void __submit_merged_bio(struct f2fs_bio_info *io)
> >>> else
> >>> trace_f2fs_submit_write_bio(io->sbi->sb, fio, io->bio);
> >>>
> >>> - __submit_bio(io->sbi, fio->rw, io->bio);
> >>> + __submit_bio(io->sbi, fio->rw, io->bio, fio->type);
> >>> io->bio = NULL;
> >>> }
> >>>
> >>> @@ -235,7 +238,7 @@ int f2fs_submit_page_bio(struct f2fs_io_info *fio)
> >>> return -EFAULT;
> >>> }
> >>>
> >>> - __submit_bio(fio->sbi, fio->rw, bio);
> >>> + __submit_bio(fio->sbi, fio->rw, bio, fio->type);
> >>> return 0;
> >>> }
> >>>
> >>> @@ -1040,7 +1043,7 @@ got_it:
> >>> */
> >>> if (bio && (last_block_in_bio != block_nr - 1)) {
> >>> submit_and_realloc:
> >>> - __submit_bio(F2FS_I_SB(inode), READ, bio);
> >>> + __submit_bio(F2FS_I_SB(inode), READ, bio, DATA);
> >>> bio = NULL;
> >>> }
> >>> if (bio == NULL) {
> >>> @@ -1083,7 +1086,7 @@ set_error_page:
> >>> goto next_page;
> >>> confused:
> >>> if (bio) {
> >>> - __submit_bio(F2FS_I_SB(inode), READ, bio);
> >>> + __submit_bio(F2FS_I_SB(inode), READ, bio, DATA);
> >>> bio = NULL;
> >>> }
> >>> unlock_page(page);
> >>> @@ -1093,7 +1096,7 @@ next_page:
> >>> }
> >>> BUG_ON(pages && !list_empty(pages));
> >>> if (bio)
> >>> - __submit_bio(F2FS_I_SB(inode), READ, bio);
> >>> + __submit_bio(F2FS_I_SB(inode), READ, bio, DATA);
> >>> return 0;
> >>> }
> >>>
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index 4a03076..67fd285 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -777,7 +777,6 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >>> {
> >>> struct page *sum_page;
> >>> struct f2fs_summary_block *sum;
> >>> - struct blk_plug plug;
> >>> unsigned int segno = start_segno;
> >>> unsigned int end_segno = start_segno + sbi->segs_per_sec;
> >>> int seg_freed = 0;
> >>> @@ -795,8 +794,6 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >>> unlock_page(sum_page);
> >>> }
> >>>
> >>> - blk_start_plug(&plug);
> >>> -
> >>> for (segno = start_segno; segno < end_segno; segno++) {
> >>> /* find segment summary of victim */
> >>> sum_page = find_get_page(META_MAPPING(sbi),
> >>> @@ -830,8 +827,6 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
> >>> f2fs_submit_merged_bio(sbi,
> >>> (type == SUM_TYPE_NODE) ? NODE : DATA, WRITE);
> >>>
> >>> - blk_finish_plug(&plug);
> >>> -
> >>> if (gc_type == FG_GC) {
> >>> while (start_segno < end_segno)
> >>> if (get_valid_blocks(sbi, start_segno++, 1) == 0)
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index 7b58bfb..eff046a 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -379,13 +379,8 @@ void f2fs_balance_fs_bg(struct f2fs_sb_info *sbi)
> >>> excess_prefree_segs(sbi) ||
> >>> excess_dirty_nats(sbi) ||
> >>> (is_idle(sbi) && f2fs_time_over(sbi, CP_TIME))) {
> >>> - if (test_opt(sbi, DATA_FLUSH)) {
> >>> - struct blk_plug plug;
> >>> -
> >>> - blk_start_plug(&plug);
> >>> + if (test_opt(sbi, DATA_FLUSH))
> >>> sync_dirty_inodes(sbi, FILE_INODE);
> >>> - blk_finish_plug(&plug);
> >>> - }
> >>> f2fs_sync_fs(sbi->sb, true);
> >>> stat_inc_bg_cp_count(sbi->stat_info);
> >>> }
> >>>
> >
> > .
> >
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