From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Daeho Jeong <daeho43@gmail.com>,
linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
Daeho Jeong <daehojeong@google.com>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix race of pending_pages in decompression
Date: Tue, 8 Dec 2020 15:55:17 -0800 [thread overview]
Message-ID: <X9ASZV4ZBBPxCpU/@google.com> (raw)
In-Reply-To: <X88ZC4f2hZxAU3C0@gmail.com>
On 12/07, Eric Biggers wrote:
> On Tue, Dec 08, 2020 at 08:51:45AM +0900, Daeho Jeong wrote:
> > > I am trying to review this but it is very hard, as the f2fs compression code is
> > > very hard to understand.
> > >
> > > It looks like a 'struct decompress_io_ctx' represents the work to decompress a
> > > particular cluster. Since the compressed data of the cluster can be read using
> > > multiple bios, there is a reference count of how many pages are remaining to be
> > > read before all the cluster's pages have been read and decompression can start.
> > >
> > > What I don't understand is why that reference counting needs to work differently
> > > depending on whether verity is enabled or not. Shouldn't it be exactly the
> > > same?
> > >
> > > There also seems to be some confusion about the scope of STEP_VERITY. Before
> > > f2fs compression was added, it was a per-bio thing. But now in a compressed
> > > file, it's really a per-cluster thing, since all decompressed pages in a
> > > compressed cluster are verified (or not verified) at once.
> > >
> > > Wouldn't it make a lot more sense to, when a cluster needs both compression and
> > > verity, *not* set STEP_VERITY on the bios, but rather set a similar flag in the
> > > decompress_io_ctx?
> > >
> >
> > Eric,
> >
> > Decompression and verity can be executed in different thread contexts
> > in different timing, so we need separate counts for each.
> >
> > We already use STEP_VERITY for non-compression case, so I think using
> > this flag in here looks more making sense.
> >
> > Thanks,
>
> That didn't really answer my questions.
>
> I gave up trying to review this patch as the compression post-read handling is
> just way too weird and hard to understand. I wrote a patch to clean it all up
> instead, please take a look:
> https://lkml.kernel.org/r/20201208060328.2237091-1-ebiggers@kernel.org
Eric,
I also tried to review your patch, but it's quite hard to follow quickly and
requires stress tests for a while. Given upcoming merge window and urgency of
the bug, let me apply Daeho's fix first. By any chance, may I ask revisiting
your clean-up on top of the fix in the next cycle?
Thanks,
>
> - Eric
next prev parent reply other threads:[~2020-12-08 23:56 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-05 4:26 [PATCH v3] f2fs: fix race of pending_pages in decompression Daeho Jeong
2020-12-07 7:05 ` [f2fs-dev] " Chao Yu
2020-12-07 7:28 ` Daeho Jeong
2020-12-07 7:41 ` Chao Yu
2020-12-07 16:42 ` Jaegeuk Kim
2020-12-07 20:31 ` Eric Biggers
2020-12-07 23:51 ` Daeho Jeong
2020-12-08 6:11 ` Eric Biggers
2020-12-08 23:55 ` Jaegeuk Kim [this message]
2020-12-09 1:34 ` Chao Yu
2020-12-09 3:15 ` Eric Biggers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=X9ASZV4ZBBPxCpU/@google.com \
--to=jaegeuk@kernel.org \
--cc=daeho43@gmail.com \
--cc=daehojeong@google.com \
--cc=ebiggers@kernel.org \
--cc=kernel-team@android.com \
--cc=linux-f2fs-devel@lists.sourceforge.net \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).