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

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Message-ID: <554ACFE8.2050908@hp.com>
Date:	Wed, 06 May 2015 22:37:28 -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 01:58 PM, Waiman Long wrote:
> 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.

It turns out that the two new patches did work on the 24-TB DragonHawk 
without the "mm: meminit: Take into account that large system caches 
scale linearly with memory" patch. The bootup time was 357s which was 
just a few seconds slower than the other bootup times that I sent you 
yesterday.

BTW, do you want to change the following log message as kswapd will no 
longer be the one doing deferred meminit?

     kswapd 0 initialised 396098436 pages in 6024ms

Cheers,
Longman

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