linux-kernel - Re: [PATCH RFC] fadvise: move active pages to inactive list with POSIX_FADV

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Message-ID: <4E085113.7060200@jp.fujitsu.com>
Date:	Mon, 27 Jun 2011 18:44:51 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	P@...igBrady.com
CC:	andrea@...terlinux.com, akpm@...ux-foundation.org,
	minchan.kim@...il.com, riel@...hat.com, peterz@...radead.org,
	hannes@...xchg.org, kamezawa.hiroyu@...fujitsu.com,
	aarcange@...hat.com, hughd@...gle.com, jamesjer@...terlinux.com,
	marcus@...ehost.com, matt@...ehost.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] fadvise: move active pages to inactive list with
 POSIX_FADV_DONTNEED

(2011/06/27 18:17), Pádraig Brady wrote:
> On 27/06/11 06:38, KOSAKI Motohiro wrote:
>>> Hmm, What if you do want to evict it from the cache for testing purposes?
>>> Perhaps this functionality should be associated with POSIX_FADV_NOREUSE?
>>> dd has been recently modified to support invalidating the cache for a file,
>>> and it uses POSIX_FADV_DONTNEED for that.
>>> http://git.sv.gnu.org/gitweb/?p=coreutils.git;a=commitdiff;h=5f311553
>>
>> This change don't break dd. dd don't have a special privilege of file cache
>> dropping if it's also used by other processes.
>>
>> if you want to drop a cache forcely (maybe for testing), you need to use
>> /proc/sys/vm/drop_caches. It's ok to ignore other processes activity because
>> it's privilege operation.
> 
> Well the function and privileges are separate things.
> I think we've agreed that the new functionality is
> best associated with POSIX_FADV_NOREUSE,
> and the existing functionality with POSIX_FADV_DONTNEED.
> 
> BTW, I don't think privileges are currently enforced
> as I got root to cache a file here with:
>   # (time md5sum; sleep 100) < big.file
> And a normal user was able to uncache with:
>   $ dd iflag=nocache if=big.file count=0
> Anyway as said, this is a separate "issue".

I'm failed to see your point. Why does dd need to ignore other
process activity? If no other process, this patch doesn't change
any behavior. Isn't it?


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