netdev - Re: [RFC] net: use atomic allocation for order-3 page allocation

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Date:	Thu, 11 Jun 2015 18:18:49 -0400
From:	Chris Mason <clm@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Shaohua Li <shli@...com>, <netdev@...r.kernel.org>,
	<davem@...emloft.net>, <Kernel-team@...com>,
	Eric Dumazet <edumazet@...gle.com>,
	David Rientjes <rientjes@...gle.com>, <linux-mm@...ck.org>
Subject: Re: [RFC] net: use atomic allocation for order-3 page allocation

On 06/11/2015 05:22 PM, Eric Dumazet wrote:
> On Thu, 2015-06-11 at 17:16 -0400, Chris Mason wrote:
>> On 06/11/2015 04:48 PM, Eric Dumazet wrote:

>>
>> networking is asking for 32KB, and the MM layer is doing what it can to
>> provide it.  Are the gains from getting 32KB contig bigger than the cost
>> of moving pages around if the MM has to actually go into compaction?
>> Should we start disk IO to give back 32KB contig?
>>
>> I think we want to tell the MM to compact in the background and give
>> networking 32KB if it happens to have it available.  If not, fall back
>> to smaller allocations without doing anything expensive.
> 
> Exactly my point. (And I mentioned this about 4 months ago)

Sorry, reading this again I wasn't very clear.  I agree with Shaohua's
patch because it is telling the allocator that we don't want to wait for
reclaim or compaction to find contiguous pages.

But, is there any fallback to a single page allocation somewhere else?
If this is the only way to get memory, we might want to add a single
alloc_page path that won't trigger compaction but is at least able to
wait for kswapd to make progress.

-chris




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