linux-kernel - Re: [PATCH -next v3 4/7] md/raid1-10: submit write io directly if bitmap is not enabled

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Date:   Wed, 31 May 2023 23:19:53 +0800
From:   Xiao Ni <xni@...hat.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     song@...nel.org, neilb@...e.de, akpm@...l.org,
        linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next v3 4/7] md/raid1-10: submit write io directly if
 bitmap is not enabled

On Wed, May 31, 2023 at 4:25 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> Hi,
>
> 在 2023/05/31 15:26, Xiao Ni 写道:
> > On Mon, May 29, 2023 at 9:14 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
> >>
> >> From: Yu Kuai <yukuai3@...wei.com>
> >>
> >> Commit 6cce3b23f6f8 ("[PATCH] md: write intent bitmap support for raid10")
> >> add bitmap support, and it changed that write io is submitted through
> >> daemon thread because bitmap need to be updated before write io. And
> >> later, plug is used to fix performance regression because all the write io
> >> will go to demon thread, which means io can't be issued concurrently.
> >>
> >> However, if bitmap is not enabled, the write io should not go to daemon
> >> thread in the first place, and plug is not needed as well.
> >>
> >> Fixes: 6cce3b23f6f8 ("[PATCH] md: write intent bitmap support for raid10")
> >> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> >> ---
> >>   drivers/md/md-bitmap.c |  4 +---
> >>   drivers/md/md-bitmap.h |  7 +++++++
> >>   drivers/md/raid1-10.c  | 13 +++++++++++--
> >>   3 files changed, 19 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
> >> index ad5a3456cd8a..3ee590cf12a7 100644
> >> --- a/drivers/md/md-bitmap.c
> >> +++ b/drivers/md/md-bitmap.c
> >> @@ -1016,7 +1016,6 @@ static int md_bitmap_file_test_bit(struct bitmap *bitmap, sector_t block)
> >>          return set;
> >>   }
> >>
> >> -
> >>   /* this gets called when the md device is ready to unplug its underlying
> >>    * (slave) device queues -- before we let any writes go down, we need to
> >>    * sync the dirty pages of the bitmap file to disk */
> >> @@ -1026,8 +1025,7 @@ void md_bitmap_unplug(struct bitmap *bitmap)
> >>          int dirty, need_write;
> >>          int writing = 0;
> >>
> >> -       if (!bitmap || !bitmap->storage.filemap ||
> >> -           test_bit(BITMAP_STALE, &bitmap->flags))
> >> +       if (!md_bitmap_enabled(bitmap))
> >>                  return;
> >>
> >>          /* look at each page to see if there are any set bits that need to be
> >> diff --git a/drivers/md/md-bitmap.h b/drivers/md/md-bitmap.h
> >> index cfd7395de8fd..3a4750952b3a 100644
> >> --- a/drivers/md/md-bitmap.h
> >> +++ b/drivers/md/md-bitmap.h
> >> @@ -273,6 +273,13 @@ int md_bitmap_copy_from_slot(struct mddev *mddev, int slot,
> >>                               sector_t *lo, sector_t *hi, bool clear_bits);
> >>   void md_bitmap_free(struct bitmap *bitmap);
> >>   void md_bitmap_wait_behind_writes(struct mddev *mddev);
> >> +
> >> +static inline bool md_bitmap_enabled(struct bitmap *bitmap)
> >> +{
> >> +       return bitmap && bitmap->storage.filemap &&
> >> +              !test_bit(BITMAP_STALE, &bitmap->flags);
> >> +}
> >> +
> >>   #endif
> >>
> >>   #endif
> >> diff --git a/drivers/md/raid1-10.c b/drivers/md/raid1-10.c
> >> index 506299bd55cb..73cc3cb9154d 100644
> >> --- a/drivers/md/raid1-10.c
> >> +++ b/drivers/md/raid1-10.c
> >> @@ -131,9 +131,18 @@ static inline bool raid1_add_bio_to_plug(struct mddev *mddev, struct bio *bio,
> >>                                        blk_plug_cb_fn unplug)
> >>   {
> >>          struct raid1_plug_cb *plug = NULL;
> >> -       struct blk_plug_cb *cb = blk_check_plugged(unplug, mddev,
> >> -                                                  sizeof(*plug));
> >> +       struct blk_plug_cb *cb;
> >> +
> >> +       /*
> >> +        * If bitmap is not enabled, it's safe to submit the io directly, and
> >> +        * this can get optimal performance.
> >> +        */
> >> +       if (!md_bitmap_enabled(mddev->bitmap)) {
> >> +               raid1_submit_write(bio);
> >> +               return true;
> >> +       }
> >
> > Can we check this out of raid1_add_bio_to_plug and call
> > raid1_submit_write directly in make_request function?
>
> Of course we can, I'm trying to avoid redundant code here...

I know. But it doesn't fit the name of the function.

Regards
Xiao
>
> Thanks,
> Kuai
> >
> > Regards
> > Xiao
> >>
> >> +       cb = blk_check_plugged(unplug, mddev, sizeof(*plug));
> >>          if (!cb)
> >>                  return false;
> >>
> >> --
> >> 2.39.2
> >>
> >
> > .
> >
>