linux-kernel - Re: [patch] android, lowmemorykiller: remove task handoff notifier

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Date:	Mon, 9 Apr 2012 18:23:02 -0700
From:	Colin Cross <ccross@...gle.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	werner <w.landgraf@...ru>, Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Rabin Vincent <rabin.vincent@...ricsson.com>,
	Christian Bejram <christian.bejram@...ricsson.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	stable@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [patch] android, lowmemorykiller: remove task handoff notifier

On Mon, Apr 9, 2012 at 4:56 PM, David Rientjes <rientjes@...gle.com> wrote:
> The task handoff notifier leaks task_struct since it never gets freed
> after the callback returns NOTIFY_OK, which means it is responsible for
> doing so.
>
> It turns out the lowmemorykiller actually doesn't need this notifier at
> all.  It's used to prevent unnecessary killing by waiting for a thread to
> exit as a result of lowmem_shrink(), however, it's possible to do this in
> the same way the kernel oom killer works by setting TIF_MEMDIE and avoid
> killing if we're still waiting for it to exit.
>
> The kernel oom killer will already automatically set TIF_MEMDIE for
> threads that are attempting to allocate memory that have a fatal signal.
> The thread selected by lowmem_shrink() will have such a signal after the
> lowmemorykiller sends it a SIGKILL, so this won't result in an
> unnecessary use of memory reserves for the thread to exit.
>
> This has the added benefit that we don't have to rely on CONFIG_PROFILING
> to prevent needlessly killing tasks.
>
> Reported-by: werner <w.landgraf@...ru>
> Cc: stable@...r.kernel.org
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  drivers/staging/android/lowmemorykiller.c |   48 +++++------------------------
>  1 file changed, 7 insertions(+), 41 deletions(-)
>

I did a quick test to measure the difference in time spent inside
lowmem_shrink with and without this patch, and they were about the
same.  So,
Acked-by: Colin Cross <ccross@...roid.com>
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