linux-kernel - Re: [PATCH 0/13] Parallel struct page initialisation v4

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Message-ID: <554A5655.6060108@hp.com>
Date:	Wed, 06 May 2015 13:58:45 -0400
From:	Waiman Long <waiman.long@...com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Nathan Zimmer <nzimmer@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Scott Norton <scott.norton@...com>,
	Daniel J Blueman <daniel@...ascale.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/13] Parallel struct page initialisation v4

On 05/06/2015 06:22 AM, Mel Gorman wrote:
> On Wed, May 06, 2015 at 08:12:46AM +0100, Mel Gorman wrote:
>> On Tue, May 05, 2015 at 03:25:49PM -0700, Andrew Morton wrote:
>>> On Tue, 5 May 2015 23:13:29 +0100 Mel Gorman<mgorman@...e.de>  wrote:
>>>
>>>>> Alternatively, the page allocator can go off and synchronously
>>>>> initialize some pageframes itself.  Keep doing that until the
>>>>> allocation attempt succeeds.
>>>>>
>>>> That was rejected during review of earlier attempts at this feature on
>>>> the grounds that it impacted allocator fast paths.
>>> eh?  Changes are only needed on the allocation-attempt-failed path,
>>> which is slow-path.
>> We'd have to distinguish between falling back to other zones because the
>> high zone is artifically exhausted and normal ALLOC_BATCH exhaustion. We'd
>> also have to avoid falling back to remote nodes prematurely. While I have
>> not tried an implementation, I expected they would need to be in the fast
>> paths unless I used jump labels to get around it. I'm going to try altering
>> when we initialise instead so that it happens earlier.
>>
> Which looks as follows. Waiman, a test on the 24TB machine would be
> appreciated again. This patch should be applied instead of "mm: meminit:
> Take into account that large system caches scale linearly with memory"
>
> ---8<---
> mm: meminit: Finish initialisation of memory before basic setup
>
> Waiman Long reported that 24TB machines hit OOM during basic setup when
> struct page initialisation was deferred. One approach is to initialise memory
> on demand but it interferes with page allocator paths. This patch creates
> dedicated threads to initialise memory before basic setup. It then blocks
> on a rw_semaphore until completion as a wait_queue and counter is overkill.
> This may be slower to boot but it's simplier overall and also gets rid of a
> lot of section mangling which existed so kswapd could do the initialisation.
>
> Signed-off-by: Mel Gorman<mgorman@...e.de>
>

This patch moves the deferred meminit from kswapd to its own kernel 
threads started after smp_init(). However, the hash table allocation was 
done earlier than that. It seems like it will still run out of memory in 
the 24TB machine that I tested on.

I will certainly try it out, but I doubt it will solve the problem on 
its own.

Cheers,
Longman


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