Date: Thu, 9 Feb 2006 20:43:14 -0800
From: Andrew Morton <akpm@osdl.org>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: linux@horizon.com, linux-kernel@vger.kernel.org, sct@redhat.com
Subject: Re: msync() behaviour broken for MS_ASYNC, revert patch?
Message-Id: <20060209204314.2dae2814.akpm@osdl.org>
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Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> > Secondly, consider the behaviour of the above application if it is modifying
>  > the same page relatively frequently (quite likely).  If MS_ASYNC starts I/O
>  > immediately, that page will get written 10, 100 or 1000 times per second. 
>  > If MS_ASYNC leaves it to pdflush, that page gets written once per 30
>  > seconds, so we do far much less I/O.
>  > 
>  > We just don't know.  It's better to leave it up to the application designer
>  > rather than lumping too many operations into the one syscall.
> 
>  Well it remains the same conceptual operation (asynchronously "schedule"
>  dirty pages for writeout). However it simply becomes more useful to start
>  the writeout immediately, given that's the (pretty explicit) hint that is
>  given to us.

If you want to start the I/O now, fine, start the I/O now.

If you don't want to start I/O now, fine, don't start I/O now.

If msync() were to unconditionally start I/O, you don't get that option.

It's pretty simple, isn't it?
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