linux-kernel - Re: [PATCH 5/7] Introduce a means of compacting memory within a zone

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Message-ID: <Pine.LNX.4.64.0706191219250.7008@schroedinger.engr.sgi.com>
Date:	Tue, 19 Jun 2007 12:20:49 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Mel Gorman <mel@...net.ie>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 5/7] Introduce a means of compacting memory within a zone

On Tue, 19 Jun 2007, Mel Gorman wrote:

> When other mechanisms exist, they would be added here. Right now,
> isolate_lru_page() is the only one I am aware of.

Did you have a look at kmem_cache_vacate in the slab defrag patchset?

> > You do not need to check the result of migration? Page migration is a best 
> > effort that may fail.

> You're right. I used to check it for debugging purposes to make sure migration
> was actually occuring. It is not unusual still for a fair number of pages
> to fail to migrate. migration already uses a retry logic and I shouldn't
> be replicating it.
> 
> More importantly, by leaving the pages on the migratelist, I potentially
> retry the same migrations over and over again wasting time and effort not
> to mention that I keep pages isolated for much longer than necessary and
> that could cause stalling problems. I should be calling putback_lru_pages()
> when migrate_pages() tells me it failed to migrate pages.

No the putback_lru is done for you.
 
> I'll revisit this one. Thanks

You could simply ignore it if you do not care if its migrated or not.

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