From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Benjamin LaHaise <bcrl@linux.intel.com>
Cc: akpm@osdl.org, linux-mm@kvack.org, netdev@vger.kernel.org
Subject: Re: [PATCH] avoid atomic op on page free
Date: Tue, 07 Mar 2006 13:14:43 +1100 [thread overview]
Message-ID: <440CEC93.9080508@yahoo.com.au> (raw)
In-Reply-To: <20060307015810.GK32565@linux.intel.com>
Benjamin LaHaise wrote:
>On Tue, Mar 07, 2006 at 12:53:27PM +1100, Nick Piggin wrote:
>
>>You can't do this because you can't test PageLRU like that.
>>
>>Have a look in the lkml archives a few months back, where I proposed
>>a way to do this for __free_pages(). You can't do it for put_page.
>>
>
>Even if we know that we are the last user of the page (the count is 1)?
>Who can bump the page's count then?
>
>
Yes. vmscan.
Your page_count and PageLRU tests have no synchronisation between
them, which is the problem AFAIKS. Anything can happen between them
and they can probably also be executed out of order (the loads).
>>BTW I have quite a large backlog of patches in -mm which should end
>>up avoiding an atomic or two around these parts.
>>
>
>That certainly looks like it will help. Not taking the spinlock
>unconditionally gets rid of quite a bit of the cost.
>
>
Cool.
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prev parent reply other threads:[~2006-03-07 2:14 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-07 0:10 Benjamin LaHaise
2006-03-07 0:50 ` Andrew Morton
2006-03-07 1:11 ` Benjamin LaHaise
2006-03-07 1:39 ` Andrew Morton
2006-03-07 1:52 ` Benjamin LaHaise
2006-03-07 6:30 ` Andi Kleen
2006-03-07 2:04 ` Nick Piggin
2006-03-07 2:10 ` Benjamin LaHaise
2006-03-07 4:08 ` Nick Piggin
2006-03-07 2:30 ` Chen, Kenneth W
2006-03-07 4:13 ` Nick Piggin
2006-03-07 1:21 ` Rick Jones
2006-03-07 1:53 ` Nick Piggin
2006-03-07 1:58 ` Benjamin LaHaise
2006-03-07 2:14 ` Nick Piggin [this message]
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