From: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
To: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Christoph Hellwig <hch@infradead.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>,
Michel Lespinasse <walken@google.com>,
Mel Gorman <mgorman@suse.de>, Lutz Vieweg <lvml@5t9.de>
Subject: Re: [PATCH] mm: preallocate page before lock_page at filemap COW. (WasRe: [PATCH V2] mm: Do not keep page locked during page fault while charging it for memcg
Date: Thu, 23 Jun 2011 22:01:40 +0900 [thread overview]
Message-ID: <BANLkTimshUCY5Yq5g9dnY0gi2TRneGscug@mail.gmail.com> (raw)
In-Reply-To: <20110623115855.GF31593@tiehlicka.suse.cz>
2011/6/23 Michal Hocko <mhocko@suse.cz>:
> On Thu 23-06-11 19:01:57, KAMEZAWA Hiroyuki wrote:
>> On Thu, 23 Jun 2011 11:02:04 +0200
>> Michal Hocko <mhocko@suse.cz> wrote:
>>
>> > On Thu 23-06-11 17:08:11, KAMEZAWA Hiroyuki wrote:
>> > > On Thu, 23 Jun 2011 09:41:33 +0200
>> > > Michal Hocko <mhocko@suse.cz> wrote:
>> > [...]
>> > > > Other than that:
>> > > > Reviewed-by: Michal Hocko <mhocko@suse.cz>
>> > > >
>> > >
>> > > I found the page is added to LRU before charging. (In this case,
>> > > memcg's LRU is ignored.) I'll post a new version with a fix.
>> >
>> > Yes, you are right. I have missed that.
>> > This means that we might race with reclaim which could evict the COWed
>> > page wich in turn would uncharge that page even though we haven't
>> > charged it yet.
>> >
>> > Can we postpone page_add_new_anon_rmap to the charging path or it would
>> > just race somewhere else?
>> >
>>
>> I got a different idea. How about this ?
>> I think this will have benefit for non-memcg users under OOM, too.
>
> Could you be more specific? I do not see how preallocation which might
> turn out to be pointless could help under OOM.
>
We'll have no page allocation under lock_page() held in this path.
I think it is good.
>>
>> A concerns is VM_FAULT_RETRY case but wait-for-lock will be much heavier
>> than preallocation + free-for-retry cost.
>
> Preallocation is rather costly when fault handler fails (e.g. SIGBUS
> which is the easiest one to trigger).
>
I think pcp cache of free page allocater does enough good job and I guess
we'll see no problem even if there is a storm of SIGBUS.
> I am not saying this approach is bad but I think that preallocation can
> be much more costly than unlock, charge and lock&recheck approach.
memcg_is_disabled() cannot help ROOT cgroup. And additional
lock/unlock method may kill FAULT_RETRY at lock contention optimization
which was added recently.
Thanks,
-Kame
--
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/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2011-06-23 13:01 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-22 12:06 [PATCH] mm: Do not keep page locked during page fault while charging it for memcg Michal Hocko
2011-06-22 12:15 ` Christoph Hellwig
2011-06-22 12:32 ` [PATCH V2] " Michal Hocko
2011-06-23 6:08 ` [PATCH] memcg: unlock page before charging it. (WasRe: " KAMEZAWA Hiroyuki
2011-06-23 7:23 ` Daisuke Nishimura
2011-06-23 7:41 ` Michal Hocko
2011-06-23 8:08 ` KAMEZAWA Hiroyuki
2011-06-23 9:02 ` Michal Hocko
2011-06-23 10:01 ` [PATCH] mm: preallocate page before lock_page at filemap COW. " KAMEZAWA Hiroyuki
2011-06-23 11:58 ` Michal Hocko
2011-06-23 13:01 ` Hiroyuki Kamezawa [this message]
2011-06-23 13:23 ` Michal Hocko
2011-06-23 13:51 ` Hiroyuki Kamezawa
2011-06-24 7:57 ` Michal Hocko
2011-06-24 11:46 ` Hiroyuki Kamezawa
2011-07-12 9:48 ` Michal Hocko
2012-01-26 10:46 ` Lutz Vieweg
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=BANLkTimshUCY5Yq5g9dnY0gi2TRneGscug@mail.gmail.com \
--to=kamezawa.hiroyuki@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=hch@infradead.org \
--cc=hughd@google.com \
--cc=kamezawa.hiroyu@jp.fujitsu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=lvml@5t9.de \
--cc=mgorman@suse.de \
--cc=mhocko@suse.cz \
--cc=riel@redhat.com \
--cc=walken@google.com \
/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).