From: Konstantin Khlebnikov <khlebnikov@openvz.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] mm: adjust rss counters for migration entiries
Date: Wed, 11 Jan 2012 12:23:11 +0400 [thread overview]
Message-ID: <4F0D46EF.4060705@openvz.org> (raw)
In-Reply-To: <20120111144125.0c61f35f.kamezawa.hiroyu@jp.fujitsu.com>
KAMEZAWA Hiroyuki wrote:
> On Fri, 06 Jan 2012 21:38:56 +0400
> Konstantin Khlebnikov<khlebnikov@openvz.org> wrote:
>
>> Memory migration fill pte with migration entry and it didn't update rss counters.
>> Then it replace migration entry with new page (or old one if migration was failed).
>> But between this two passes this pte can be unmaped, or task can fork child and
>> it will get copy of this migration entry. Nobody account this into rss counters.
>>
>> This patch properly adjust rss counters for migration entries in zap_pte_range()
>> and copy_one_pte(). Thus we avoid extra atomic operations on migration fast-path.
>>
>> Signed-off-by: Konstantin Khlebnikov<khlebnikov@openvz.org>
>
> It's better to show wheter this is a bug-fix or not in changelog.
>
> IIUC, the bug-fix is the 1st harf of this patch + patch [2/3].
> Your new bug-check code is in patch[1/3] and 2nd half of this patch.
>
No, there only one new bug-check in 1st patch, this is non-fatal warning.
I didn't hide this check under CONFIG_VM_DEBUG because it rather small and
rss counters covers whole page-table management, this is very good invariant.
Currently I can trigger this warning only on this rare race -- extremely loaded
memory compaction catches this every several seconds.
1/3 bug-check
2/3 fix preparation
3/3 bugfix in two places:
do rss++ in copy_one_pte()
do rss-- in zap_pte_range()
> I think it's better to do bug-fix 1st and add bug-check later.
>
> So, could you reorder patches to bug-fix and new-bug-check ?
Patches didn't share any context, so they can be applied in any order.
>
> To the logic itself,
> Acked-by: KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com>
> Please CC when you repost.
>
>
>
next prev parent reply other threads:[~2012-01-11 8:23 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-06 17:38 [PATCH 1/3] mm: add rss counters consistency check Konstantin Khlebnikov
2012-01-06 17:38 ` [PATCH 2/3] mm: postpone migrated page mapping reset Konstantin Khlebnikov
2012-01-06 17:38 ` [PATCH 3/3] mm: adjust rss counters for migration entiries Konstantin Khlebnikov
2012-01-06 17:45 ` Konstantin Khlebnikov
2012-01-11 5:41 ` KAMEZAWA Hiroyuki
2012-01-11 8:23 ` Konstantin Khlebnikov [this message]
2012-01-11 8:41 ` KAMEZAWA Hiroyuki
2012-01-18 23:21 ` Andrew Morton
2012-01-24 1:42 ` Hugh Dickins
2012-01-24 7:08 ` Konstantin Khlebnikov
2012-01-25 23:01 ` Hugh Dickins
2012-01-26 0:20 ` Andrew Morton
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