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Date: Tue, 8 Mar 2011 21:47:08 -0500
From: Stephen Wilson <wilsons@start.ca>
Subject: Re: [PATCH 0/6] enable writing to /proc/pid/mem
Message-ID: <20110309024708.GA4941@fibrous.localdomain>
References: <1299631343-4499-1-git-send-email-wilsons@start.ca> <20110309013017.GY22723@ZenIV.linux.org.uk> <20110309021524.GA4838@fibrous.localdomain> <20110309023303.GZ22723@ZenIV.linux.org.uk>
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To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Roland McGrath <roland@redhat.com>, Matt Mackall <mpm@selenic.com>, David Rientjes <rientjes@google.com>, Nick Piggin <npiggin@kernel.dk>, Andrea Arcangeli <aarcange@redhat.com>, Mel Gorman <mel@csn.ul.ie>, Ingo Molnar <mingo@elte.hu>, Michel Lespinasse <walken@google.com>, Hugh Dickins <hughd@google.com>, linux-kernel@vger.kernel.org

On Wed, Mar 09, 2011 at 02:33:04AM +0000, Al Viro wrote:
> On Tue, Mar 08, 2011 at 09:15:25PM -0500, Stephen Wilson wrote:
> 
> > I think we could also remove the intermediate copy in both mem_read() and
> > mem_write() as well, but I think such optimizations could be left for
> > follow on patches.
> 
> How?  We do copy_.._user() in there; it can trigger page faults and
> that's not something you want while holding mmap_sem on some mm.

Ah, OK.   I did not think thru that subtlety.  Was merely mentioning
"things we might do afterwords" as opposed to a genuine proposal.

> Looks like a deadlock country...  So we can't do that from inside
> access_process_vm() or its analogs, which means buffering in caller.

Thanks for the feed back -- I am certainly (relatively speaking) new to
the code so your insights are most valuable.

Thanks again!


-- 
steve

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