linux-kernel - Re: [PATCH] MM: implement MADV_FREE lazy freeing of anonymous memory

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Message-ID: <4641065D.6060403@yahoo.com.au>
Date:	Wed, 09 May 2007 09:23:09 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Rik van Riel <riel@...hat.com>
CC:	Ulrich Drepper <drepper@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jakub Jelinek <jakub@...hat.com>
Subject: Re: [PATCH] MM: implement MADV_FREE lazy freeing of anonymous memory

Rik van Riel wrote:
> Nick Piggin wrote:
> 
>> We have percpu and cache affine page allocators, so when
>> userspace just frees a page, it is likely to be cache hot, so
>> we want to free it up so it can be reused by this CPU ASAP.
>> Likewise, when we newly allocate a page, we want it to be one
>> that is cache hot on this CPU.
> 
> 
> Actually, isn't the clear page function capable of doing
> some magic, when it writes all zeroes into the page, that
> causes the zeroes to just live in CPU cache without the old
> data ever being loaded from RAM?
> 
> That would sure be faster than touching RAM.  Not sure if
> we use/trigger that kind of magic, though :)
> 

powerpc has and uses an instruction to zero a full cacheline, yes.

Not sure about x86-64 CPUs... I don't think they can do it.

-- 
SUSE Labs, Novell Inc.
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