Re: [resend] [PATCH] mm: vmscan: fix do_try_to_free_pages() livelock

[Minchan Kim <minchan@kernel.org>]

On Sun, Aug 04, 2013 at 07:26:38PM -0700, Lisa Du wrote:
> From: Lisa Du <cldu@marvell.com>
> Date: Mon, 5 Aug 2013 09:26:57 +0800
> Subject: [PATCH] mm: vmscan: fix do_try_to_free_pages() livelock
> 
> This patch is based on KOSAKI's work and I add a little more
> description, please refer https://lkml.org/lkml/2012/6/14/74.
> 
> Currently, I found system can enter a state that there are lots
> of free pages in a zone but only order-0 and order-1 pages which
> means the zone is heavily fragmented, then high order allocation
> could make direct reclaim path's long stall(ex, 60 seconds)
> especially in no swap and no compaciton enviroment. This problem
> happened on v3.4, but it seems issue still lives in current tree,
> the reason is do_try_to_free_pages enter live lock:
> 
> kswapd will go to sleep if the zones have been fully scanned
> and are still not balanced. As kswapd thinks there's little point
> trying all over again to avoid infinite loop. Instead it changes
> order from high-order to 0-order because kswapd think order-0 is the
> most important. Look at 73ce02e9 in detail. If watermarks are ok,
> kswapd will go back to sleep and may leave zone->all_unreclaimable = 0.
> It assume high-order users can still perform direct reclaim if they wish.
> 
> Direct reclaim continue to reclaim for a high order which is not a
> COSTLY_ORDER without oom-killer until kswapd turn on zone->all_unreclaimble.
> This is because to avoid too early oom-kill. So it means direct_reclaim
> depends on kswapd to break this loop.
> 
> In worst case, direct-reclaim may continue to page reclaim forever
> when kswapd sleeps forever until someone like watchdog detect and finally
> kill the process. As described in:
> http://thread.gmane.org/gmane.linux.kernel.mm/103737
> 
> We can't turn on zone->all_unreclaimable from direct reclaim path
> because direct reclaim path don't take any lock and this way is racy.
> Thus this patch removes zone->all_unreclaimable field completely and
> recalculates zone reclaimable state every time.
> 
> Note: we can't take the idea that direct-reclaim see zone->pages_scanned
> directly and kswapd continue to use zone->all_unreclaimable. Because, it
> is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use
> zone->all_unreclaimable as a name) describes the detail.
> 
> Change-Id: If3b44e33e400c1db0e42a5e2fc9ebc7a265f2aae

Please remove this line and It seems to go with stable if others agree.
Otherwise, looks good to me.

Acked-by: Minchan Kim <minchan@kernel.org>

-- 
Kind regards,
Minchan Kim

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