linux-kernel - Re: [PATCH] mm: Enable MAP_UNINITIALIZED for archs with mmu

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Message-ID: <4F1F5EB8.3000407@fb.com>
Date:	Tue, 24 Jan 2012 17:45:28 -0800
From:	Arun Sharma <asharma@...com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	Balbir Singh <bsingharora@...il.com>,
	<akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: Enable MAP_UNINITIALIZED for archs with mmu

On 1/23/12 7:07 PM, KAMEZAWA Hiroyuki wrote:

> You can see reduction of clear_page() cost by removing GFP_ZERO but
> what's your application's total performance ? Is it good enough considering
> many risks ?

I see 90k calls/sec to clear_page_c when running our application. I 
don't have data on the impact of GFP_ZERO alone, but an earlier 
experiment when we tuned malloc to not call madvise(MADV_DONTNEED) 
aggressively saved us 3% CPU. So I'm expecting this to be a 1-2% win.

But not calling madvise() increases our RSS and increases the risk of OOM.

Agree with your analysis that removing the cache misses at clear_page() 
is not always a win, since it moves the misses to the code where the app 
first touches the data.

  -Arun

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