linux-kernel - Re: [RFC 1/2] deactive invalidated pages

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Message-ID: <87hbf89jfk.fsf@gmail.com>
Date:	Tue, 23 Nov 2010 09:57:35 -0500
From:	Ben Gamari <bgamari@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [RFC 1/2] deactive invalidated pages

On Tue, 23 Nov 2010 16:16:55 +0900 (JST), KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> > By Other approach, app developer uses POSIX_FADV_DONTNEED.
> > But it has a problem. If kernel meets page is writing
> > during invalidate_mapping_pages, it can't work.
> > It is very hard for application programmer to use it.
> > Because they always have to sync data before calling
> > fadivse(..POSIX_FADV_DONTNEED) to make sure the pages could
> > be discardable. At last, they can't use deferred write of kernel
> > so that they could see performance loss.
> > (http://insights.oetiker.ch/linux/fadvise.html)
> 
> If rsync use the above url patch, we don't need your patch. 
> fdatasync() + POSIX_FADV_DONTNEED should work fine.
> 
This is quite true, but the patch itself is fairly invasive and
unnecessarily so which makes it unsuitable for merging in the eyes of
the rsync maintainers (not that I can blame them). This is by no fault
of its author; using fadvise is just far harder than it should be.

- Ben
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