linux-kernel - Re: [PATCH 3/3] vmevent: Implement special low-memory attribute

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Date:	Mon, 7 May 2012 04:26:00 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Minchan Kim <minchan@...nel.org>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH 3/3] vmevent: Implement special low-memory attribute

>> If we'll give up on "1." (Pekka, ping), then we need to solve "2."
>> in a sane way: we'll have to add a 'NR_FILE_PAGES - NR_SHMEM -
>> <todo-locked-file-pages>' attribute, and give it a name.
>
> Well, no, we can't give up on (1) completely. That'd mean that
> eventually we'd need to change the ABI and break userspace. The
> difference between exposing internal details and reasonable
> abstractions is by no means black and white.
>
> AFAICT, RECLAIMABLE_CACHE_PAGES is a reasonable thing to support. Can
> anyone come up with a reason why we couldn't do that in the future?

It can. but the problem is, that is completely useless. Because of, 1)
dirty pages writing-out
is sometimes very slow and 2) libc and some important library's pages
are critical important
for running a system even though it is clean and reclaimable. In other
word, kernel don't have
an info then can't expose it.
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