linux-kernel - Re: [PATCH]mmap: avoid unnecessary anon

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Message-ID: <m2fwq718u4.fsf@firstfloor.org>
Date:	Mon, 28 Mar 2011 09:57:39 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH]mmap: avoid unnecessary anon_vma lock

Shaohua Li <shaohua.li@...el.com> writes:

> If we only change vma->vm_end, we can avoid taking anon_vma lock even 'insert'
> isn't NULL, which is the case of split_vma.
> From my understanding, we need the lock before because rmap must get the
> 'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked to
> anon_vma list in __insert_vm_struct before).
> But now this isn't true any more. The 'insert' VMA is already linked to
> anon_vma list in __split_vma(with anon_vma_clone()) instead of
> __insert_vm_struct. There is no race rmap can't get required VMAs.
> So the anon_vma lock is unnecessary, and this can reduce one locking in brk
> case and improve scalability.

Looks good to me.
-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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