linux-kernel - Re: [PATCH] lazy freeing of memory through MADV

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Date:	Sun, 22 Apr 2007 01:18:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] lazy freeing of memory through MADV_FREE

On Tue, 17 Apr 2007 03:15:51 -0400 Rik van Riel <riel@...hat.com> wrote:

> Make it possible for applications to have the kernel free memory
> lazily.  This reduces a repeated free/malloc cycle from freeing
> pages and allocating them, to just marking them freeable.  If the
> application wants to reuse them before the kernel needs the memory,
> not even a page fault will happen.
> 
> This patch, together with Ulrich's glibc change, increases
> MySQL sysbench performance by a factor of 2 on my quad core
> test system.
> 

In file included from include/linux/mman.h:4,
                 from arch/sparc64/kernel/sys_sparc.c:19:
include/asm/mman.h:36:1: "MADV_FREE" redefined
In file included from include/asm/mman.h:5,
                 from include/linux/mman.h:4,
                 from arch/sparc64/kernel/sys_sparc.c:19:
include/asm-generic/mman.h:32:1: this is the location of the previous definition

sparc32 and sparc64 already defined MADV_FREE:


#define MADV_FREE       0x5             /* (Solaris) contents can be freed */

I'll remove the sparc definitions for now, but we need to work out what
we're going to do here.  Your patch changes the values of MADV_FREE on
sparc.

Perhaps this should be renamed to MADV_FREE_LINUX and given a different
number.  It depends on how close your proposed behaviour is to Solaris's.

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