From: Andrew Morton <akpm@linux-foundation.org>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Michal Hocko <mhocko@suse.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] proc/kpageflags: add KPF_WAITERS
Date: Tue, 20 Feb 2018 16:00:34 -0800 [thread overview]
Message-ID: <20180220160034.db7a3122c44e274ef562002e@linux-foundation.org> (raw)
In-Reply-To: <cd7b5099-0575-81ce-9f48-2efd664f2fc2@yandex-team.ru>
On Sat, 17 Feb 2018 11:14:10 +0300 Konstantin Khlebnikov <khlebnikov@yandex-team.ru> wrote:
> On 17.02.2018 02:57, Andrew Morton wrote:
> > On Sun, 11 Feb 2018 13:36:41 +0300 Konstantin Khlebnikov <khlebnikov@yandex-team.ru> wrote:
> >
> >> KPF_WAITERS indicates tasks are waiting for a page lock or writeback.
> >> This might be false-positive, in this case next unlock will clear it.
> >
> > Well, kpageflags is full of potential false-positives. Or do you think
> > this flag is especially vulnerable?
> >
> > In other words, under what circumstances will we have KPF_WAITERS set
> > when PG_locked and PG-writeback are clear?
>
> Looks like lock_page() - unlock_page() shouldn't leave longstanding
> false-positive: last unlock_page() must clear PG_waiters.
>
> But I've seen them. Probably that was from wait_on_page_writeback():
> it test PG_writeback, set PG_waiters under queue lock unconditionally
> and then test PG_writeback again before sleep - and might exit
> without wakeup i.e. without clearing PG_waiters.
>
> This could be fixed with extra check for in wait_on_page_bit_common()
> under queue lock.
>
> ...
>
> This bit tells which page or D 3/4 ffset in file is actually wanted
> by somebody in the system. That's another way to track where major
> faults or writeback blocks something. We don't have to record flow
> of events - snapshot of page-flags will show where contention is.
>
Please send a v2 and let's get all this info into the changelog?
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2018-02-21 0:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-11 10:36 [PATCH] proc/kpageflags: add KPF_WAITERS Konstantin Khlebnikov
2018-02-16 23:57 ` Andrew Morton
2018-02-17 8:14 ` Konstantin Khlebnikov
2018-02-21 0:00 ` Andrew Morton [this message]
2018-02-17 8:15 ` [PATCH] Documentation/vm/pagemap.txt: document bit WAITERS Konstantin Khlebnikov
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=20180220160034.db7a3122c44e274ef562002e@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=khlebnikov@yandex-team.ru \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=n-horiguchi@ah.jp.nec.com \
--cc=npiggin@gmail.com \
--cc=torvalds@linux-foundation.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).