Date: Thu, 9 Feb 2006 19:50:35 -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?
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Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>  > It's a bit of a disaster if you happen to msync(MS_ASYNC) the same page at
>  > any sort of frequency - we have to wait for the previous I/O to complete
>  > before new I/O can be started.  That was the main problem which caused this
>  > change to be made.  You can see that it'd make 100x or 1000x speed improvements
>  > with some sane access patterns.
>  > 
> 
>  I'm not sure you'd have to do that, would you? Just move the dirty bit
>  from the pte and skip the page if it is found locked or writeback.

That would make MS_ASYNC mean "start I/O now, unless there's I/O in
progress, in whch case start I/O in 30 seconds.  That's not good.

If we're going to change the kernel, better off using fadvise()
enhancements, whic are also useful for post-write() operations.

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