linux-kernel - Re: [PATCH 1/3] revoke: misc fixes

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Message-ID: <45FA4C59.1000908@yahoo.com.au>
Date:	Fri, 16 Mar 2007 18:50:49 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Pekka J Enberg <penberg@...helsinki.fi>
CC:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] revoke: misc fixes

Pekka J Enberg wrote:
> Hi Nick,
> 
> On Fri, 16 Mar 2007, Nick Piggin wrote:
> 
>>Could you try something like walk the i_mmap lists to find mms with vmas that
>>haven't need revoking, then each time you find one, take a ref on the mm, drop
>>i_mmap_lock, take mmap_sem, and walk all its vmas looking for any that
>>reference the inode?
> 
> 
> Yes, that would work. What I am cooking up now is dropping 
> ->i_mmap_lock, restarting the scan after each revoke_vma() and skipping 
> vmas that are VM_REVOKED.

Of course you can't take a reference to a vma, so to pin a vma you need
the mmap_sem, and to do that you need to drop i_mmap_lock, which means
your vma might go away ;)

So I think you really do need to get back to the mm, and then search its
vmas.

Also, a down_write_trylock attempt inside i_mmap_lock should be a valid
optimisation.

-- 
SUSE Labs, Novell Inc.
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