linux-kernel - Re: Regression from 2.6.36

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Message-ID: <BANLkTincoaxp5Soe6O-eb8LWpgra=k2NsQ@mail.gmail.com>
Date:	Wed, 13 Apr 2011 09:23:11 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Jiri Slaby <jslaby@...e.cz>, azurIt <azurit@...ox.sk>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, Jiri Slaby <jirislaby@...il.com>
Subject: Re: Regression from 2.6.36

On Wed, Apr 13, 2011 at 6:49 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> It's somewhat unclear (to me) what caused this regression.
>
> Is it because the kernel is now doing large kmalloc()s for the fdtable,
> and this makes the page allocator go nuts trying to satisfy high-order
> page allocation requests?
>
> Is it because the kernel now will usually free the fdtable
> synchronously within the rcu callback, rather than deferring this to a
> workqueue?
>
> The latter seems unlikely, so I'm thinking this was a case of
> high-order-allocations-considered-harmful?
>

Maybe, but I am not sure. Maybe my patch causes too many inner
fragments. For example, when asking for 5 pages, get 8 pages, and 3
pages are wasted, then memory thrash happens finally.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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