Re: [PATCH 3/3] mm: adjust rss counters for migration entiries
From: Konstantin Khlebnikov
Date: Wed Jan 11 2012 - 03:23:19 EST
KAMEZAWA Hiroyuki wrote:
On Fri, 06 Jan 2012 21:38:56 +0400
Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx> 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@xxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Please CC when you repost.
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