linux-kernel - Re: [PATCH 1/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing the wrong VMA information

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Date:	Sat, 8 May 2010 12:51:08 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
cc:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/2] mm,migration: Prevent rmap_walk_[anon|ksm] seeing
 the wrong VMA information

On Sat, 8 May 2010, Andrea Arcangeli wrote:
> 
> There is no broken (as in kernel crashing) locking in my THP
> patches.

It's not about crashing. It's about being a totally unmaintainable mess, 
with ad-hoc temporary allocations, and loops over an unknown number of 
spinlocks.

That's _broken_. B. R. O. K. E. N.

And in all cases there are fixes that I've pointed out. If you can't see 
that, then that's _your_ problem. If you (or others) want your code 
merged, then it had better _fix_ the total disaster before merging. It's 
that simple.

The "lock root" thing you complain should also be easily fixable, by 
keeping the root lock a separate issue from walking the actual anon_vma 
(ie walk the anon_vma, but lock the root). You still don't have to lock 
the whole list.

			Linus
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