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

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Date:	Wed, 07 Mar 2007 09:38:34 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	mingo@...e.hu
CC:	npiggin@...e.de, akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, benh@...nel.crashing.org
Subject: Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

> > 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)

That would make sense.  Dirty page accounting doesn't work either on
non-linear mappings, and I can't see how that could be fixed in any
other way.

Miklos
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