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SubjectRE: [f2fs-dev] [PATCH 3/7] f2fs: drop any block plugging
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Thanks Kim, it'll be very meaningful in block layer :-)

-----Original Message-----
From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
Sent: 2016年7月14日 10:40
To: hebiao (G) <hebiao6@huawei.com>
Cc: Yuchao (T) <yuchao0@huawei.com>; linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux-f2fs-devel@lists.sourceforge.net; CHEN CHUN YEN (IAN) <chen.chun.yen@huawei.com>; Kongfei <kongfei@hisilicon.com>
Subject: Re: [f2fs-dev] [PATCH 3/7] f2fs: drop any block plugging

Hi hebiao,

On Wed, Jul 13, 2016 at 01:21:15AM +0000, hebiao (G) wrote:
> Hi, Kim,
>
> You are right. If file system can merge bios as much as possible. It's very helpful to block layer. But plugging mechanism has a precognition of IO stream except merging bios. For example, we can out the low-power mode in advance when you start a plug and we can in the low-power mode only when you end a plug to avoid in-out low-power mode frequently. So I want to know if there is any side effect in F2FS to reserve the plug mechanism ?

Oh, does android kernel act like that?
Nevertheless, I'll take a look at any performance regression if I add plugs in all the IO submission again.

Thanks,

>
> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@kernel.org]
> Sent: 2016年7月13日 1:08
> To: Yuchao (T) <yuchao0@huawei.com>
> Cc: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
> linux-f2fs-devel@lists.sourceforge.net; CHEN CHUN YEN (IAN)
> <chen.chun.yen@huawei.com>; hebiao (G) <hebiao6@huawei.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@kernel.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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