linux-kernel - Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

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Message-ID: <20070307082755.GA25733@elte.hu>
Date:	Wed, 7 Mar 2007 09:27:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)


* Nick Piggin <npiggin@...e.de> wrote:

> If it doesn't look very impressive, it could be because it leaves all 
> the old crud around for backwards compatibility (the worst offenders 
> are removed in patch 6/6).
> 
> If you look at the patchset as a whole, it removes about 250 lines, 
> mostly of (non trivial) duplicated code in filemap.c memory.c shmem.c 
> fremap.c, that is nonlinear pages specific and doesn't get anywhere 
> near the testing that the linear fault path does.
> 
> A minimal fix for nonlinear pages would have required changing all 
> ->populate handlers, which I simply thought was not very productive 
> considering the testing and coverage issues, and that I was going to 
> rewrite the nonlinear path anyway.
> 
> If you like, you can consider patches 1,2,3 as the fix, and ignore 
> nonlinear (hey, it doesn't even bother checking truncate_count 
> today!).
> 
> Then 4,5,6 is the fault/nonlinear rewrite, take it or leave it. I 
> thought you would have liked the patches...

btw., if we decide that nonlinear isnt worth the continuing maintainance 
pain, we could internally implement/emulate sys_remap_file_pages() via a 
call to mremap() and essentially deprecate it, without breaking the ABI 
- and remove all the nonlinear code. (This would split fremap areas into 
separate vmas)

	Ingo
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