From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: kernel-team@android.com, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: avoid readahead race condition
Date: Tue, 30 Jun 2020 13:56:35 -0700 [thread overview]
Message-ID: <20200630205635.GB1396584@google.com> (raw)
In-Reply-To: <20200630204348.GA2504307@ubuntu-s3-xlarge-x86>
On 06/30, Nathan Chancellor wrote:
> On Mon, Jun 29, 2020 at 01:27:20PM -0700, Jaegeuk Kim wrote:
> > If two readahead threads having same offset enter in readpages, every read
> > IOs are split and issued to the disk which giving lower bandwidth.
> >
> > This patch tries to avoid redundant readahead calls.
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> > v3:
> > - use READ|WRITE_ONCE
> > v2:
> > - add missing code to bypass read
> >
> > fs/f2fs/data.c | 18 ++++++++++++++++++
> > fs/f2fs/f2fs.h | 1 +
> > fs/f2fs/super.c | 2 ++
> > 3 files changed, 21 insertions(+)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 995cf78b23c5e..360b4c9080d97 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -2296,6 +2296,7 @@ static int f2fs_mpage_readpages(struct inode *inode,
> > unsigned nr_pages = rac ? readahead_count(rac) : 1;
> > unsigned max_nr_pages = nr_pages;
> > int ret = 0;
> > + bool drop_ra = false;
> >
> > map.m_pblk = 0;
> > map.m_lblk = 0;
> > @@ -2306,10 +2307,24 @@ static int f2fs_mpage_readpages(struct inode *inode,
> > map.m_seg_type = NO_CHECK_TYPE;
> > map.m_may_create = false;
> >
> > + /*
> > + * Two readahead threads for same address range can cause race condition
> > + * which fragments sequential read IOs. So let's avoid each other.
> > + */
> > + if (rac && readahead_count(rac)) {
> > + if (READ_ONCE(F2FS_I(inode)->ra_offset) == readahead_index(rac))
> > + drop_ra = true;
> > + else
> > + WRITE_ONCE(F2FS_I(inode)->ra_offset,
> > + readahead_index(rac));
> > + }
> > +
> > for (; nr_pages; nr_pages--) {
> > if (rac) {
> > page = readahead_page(rac);
> > prefetchw(&page->flags);
> > + if (drop_ra)
> > + goto next_page;
>
> When CONFIG_F2FS_FS_COMPRESSION is not set (i.e. x86_64 defconfig +
> CONFIG_F2FS_FS=y):
>
> $ make -skj"$(nproc)" O=out distclean defconfig fs/f2fs/data.o
> ../fs/f2fs/data.c: In function ‘f2fs_mpage_readpages’:
> ../fs/f2fs/data.c:2327:5: error: label ‘next_page’ used but not defined
> 2327 | goto next_page;
> | ^~~~
> ...
Thanks. I pushed the fix for -next.
https://lore.kernel.org/linux-f2fs-devel/1be18397-7fc6-703e-121b-e210e101357f@infradead.org/T/#t
Thanks,
>
> Cheers,
> Nathan
>
>
> _______________________________________________
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
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next prev parent reply other threads:[~2020-06-30 20:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 1:21 [f2fs-dev] [PATCH] f2fs: avoid readahead race condition Jaegeuk Kim
2020-06-28 2:35 ` Chao Yu
2020-06-29 15:03 ` [f2fs-dev] [PATCH v2] " Jaegeuk Kim
2020-06-29 16:09 ` Eric Biggers
2020-06-29 18:24 ` Jaegeuk Kim
2020-06-29 18:25 ` Eric Biggers
2020-06-29 20:27 ` [f2fs-dev] [PATCH v3] " Jaegeuk Kim
2020-06-30 20:43 ` Nathan Chancellor
2020-06-30 20:56 ` Jaegeuk Kim [this message]
2020-07-01 1:59 ` Chao Yu
2020-07-01 7:47 ` Chao Yu
2020-07-01 16:14 ` Jaegeuk Kim
2020-07-03 1:34 ` Chao Yu
2020-07-01 16:14 ` [f2fs-dev] [PATCH v4] " Jaegeuk Kim
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