linux-kernel - Re: [PATCH 1/4] mm/rmap: per anon

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Message-ID: <20131101120745.GC10651@twins.programming.kicks-ass.net>
Date:	Fri, 1 Nov 2013 13:07:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Cc:	Michel Lespinasse <walken@...gle.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 1/4] mm/rmap: per anon_vma lock

On Fri, Nov 01, 2013 at 07:44:29PM +0800, Yuanhan Liu wrote:
> commit 012f18004da33ba672e3c60838cc4898126174d3
> Author: Rik van Riel <riel@...hat.com>
> Date:   Mon Aug 9 17:18:40 2010 -0700
> 
>     mm: always lock the root (oldest) anon_vma
> 
>     Always (and only) lock the root (oldest) anon_vma whenever we do something
>     in an anon_vma.  The recently introduced anon_vma scalability is due to
>     the rmap code scanning only the VMAs that need to be scanned.  Many common
>     operations still took the anon_vma lock on the root anon_vma, so always
>     taking that lock is not expected to introduce any scalability issues.
> 
>     However, always taking the same lock does mean we only need to take one
>     lock, which means rmap_walk on pages from any anon_vma in the vma is
>     excluded from occurring during an munmap, expand_stack or other operation
>     that needs to exclude rmap_walk and similar functions.
> 
>     Also add the proper locking to vma_adjust.
> 
>     Signed-off-by: Rik van Riel <riel@...hat.com>
>     Tested-by: Larry Woodman <lwoodman@...hat.com>
>     Acked-by: Larry Woodman <lwoodman@...hat.com>
>     Reviewed-by: Minchan Kim <minchan.kim@...il.com>
>     Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>     Acked-by: Mel Gorman <mel@....ul.ie>
>     Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>
>     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>

Right that commit did. I'm still not sure why you change both the
locking proper and the locking primitive used in one patch set.

Also, changing the locking proper requires a very detailed explanation
on why it is correct; we've had far too many 'fun' issues with the
anon_vma locking in the past.
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