From: Rik van Riel <riel@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Ingo Molnar <mingo@kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
Mel Gorman <mel@csn.ul.ie>,
Linux kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: question on NUMA page migration
Date: Fri, 19 Oct 2012 13:13:37 -0400 [thread overview]
Message-ID: <50818A41.7030909@redhat.com> (raw)
In-Reply-To: <1350664742.2768.40.camel@twins>
On 10/19/2012 12:39 PM, Peter Zijlstra wrote:
> On Fri, 2012-10-19 at 11:53 -0400, Rik van Riel wrote:
>>
>> If we do need the extra refcount, why is normal
>> page migration safe? :)
>
> Its mostly a matter of how convoluted you make the code, regular page
> migration is about as bad as you can get
>
> Normal does:
>
> follow_page(FOLL_GET) +1
>
> isolate_lru_page() +1
>
> put_page() -1
>
> ending up with a page with a single reference (for anon, or one extra
> each for the mapping and buffer).
Would it make sense to have the normal page migration code always
work with the extra refcount, so we do not have to introduce a new
MIGRATE_FAULT migration mode?
On the other hand, compaction does not take the extra reference...
Another alternative might be to do the put_page inside
do_prot_none_numa(). That would be analogous to do_wp_page
disposing of the old page for the caller.
I am not real happy about NUMA migration introducing its own
migration mode...
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WARNING: multiple messages have this Message-ID (diff)
From: Rik van Riel <riel@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Ingo Molnar <mingo@kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
Mel Gorman <mel@csn.ul.ie>,
Linux kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: question on NUMA page migration
Date: Fri, 19 Oct 2012 13:13:37 -0400 [thread overview]
Message-ID: <50818A41.7030909@redhat.com> (raw)
In-Reply-To: <1350664742.2768.40.camel@twins>
On 10/19/2012 12:39 PM, Peter Zijlstra wrote:
> On Fri, 2012-10-19 at 11:53 -0400, Rik van Riel wrote:
>>
>> If we do need the extra refcount, why is normal
>> page migration safe? :)
>
> Its mostly a matter of how convoluted you make the code, regular page
> migration is about as bad as you can get
>
> Normal does:
>
> follow_page(FOLL_GET) +1
>
> isolate_lru_page() +1
>
> put_page() -1
>
> ending up with a page with a single reference (for anon, or one extra
> each for the mapping and buffer).
Would it make sense to have the normal page migration code always
work with the extra refcount, so we do not have to introduce a new
MIGRATE_FAULT migration mode?
On the other hand, compaction does not take the extra reference...
Another alternative might be to do the put_page inside
do_prot_none_numa(). That would be analogous to do_wp_page
disposing of the old page for the caller.
I am not real happy about NUMA migration introducing its own
migration mode...
--
All rights reversed
next prev parent reply other threads:[~2012-10-19 17:13 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-19 15:53 question on NUMA page migration Rik van Riel
2012-10-19 15:53 ` Rik van Riel
2012-10-19 16:39 ` Peter Zijlstra
2012-10-19 16:39 ` Peter Zijlstra
2012-10-19 17:13 ` Rik van Riel [this message]
2012-10-19 17:13 ` Rik van Riel
2012-10-19 17:53 ` Peter Zijlstra
2012-10-19 17:53 ` Peter Zijlstra
2012-10-19 18:33 ` Rik van Riel
2012-10-19 18:33 ` Rik van Riel
2012-10-20 1:23 ` Ingo Molnar
2012-10-20 1:23 ` Ingo Molnar
2012-10-20 16:02 ` Rik van Riel
2012-10-20 16:02 ` Rik van Riel
2012-10-21 12:30 ` Ingo Molnar
2012-10-21 12:30 ` Ingo Molnar
2012-10-21 2:39 ` Ni zhan Chen
2012-10-21 2:39 ` Ni zhan Chen
2012-10-21 2:40 ` Rik van Riel
2012-10-21 2:40 ` Rik van Riel
2012-10-21 12:31 ` Ingo Molnar
2012-10-21 12:31 ` Ingo Molnar
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