Re: [PATCH 12/12] mm, page_alloc: Only enforce watermarks for order-0 allocations

From: Vlastimil Babka <vbabka@suse.cz>
To: Vitaly Wool <vitalywool@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>,
	Joonsoo Kim <js1304@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Rik van Riel <riel@redhat.com>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Michal Hocko <mhocko@kernel.org>, Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 12/12] mm, page_alloc: Only enforce watermarks for order-0 allocations
Date: Wed, 30 Sep 2015 16:43:00 +0200	[thread overview]
Message-ID: <560BF4F4.9010000@suse.cz> (raw)
In-Reply-To: <CAMJBoFOKGchN7LQny+tsWd-wL0LVyt8NL+7FZE__TvskanFhsg@mail.gmail.com>

On 09/30/2015 04:16 PM, Vitaly Wool wrote:
>>>>>
>>>>
>>>> So what do you suggest instead? A fixed number, some other heuristic?
>>>> You have pushed several times now for the series to focus on the latency
>>>> of standard high-order allocations but again I will say that it is
>>>> outside
>>>> the scope of this series. If you want to take steps to reduce the latency
>>>> of ordinary high-order allocation requests that can sleep then it should
>>>> be a separate series.
>>>
>>>
>>> I do believe https://lkml.org/lkml/2015/9/9/313 does a better job
>>
>>
>> Does a better job regarding what exactly? It does fix the CMA-specific
>> issue, but so does this patch - without affecting allocation fastpaths by
>> making them update another counter. But the issues discussed here are not
>> related to that CMA problem.
>
> Let me disagree. Guaranteeing one suitable high-order page is not
> enough, so the suggested patch does not work that well for me.
> Existing broken watermark calculation doesn't work for me either, as
> opposed to the one with my patch applied. Both solutions are related
> to the CMA issue but one does make compaction work harder and cause
> bigger latencies -- why do you think these are not related?

Well you didn't mention which issues you have with this patch. If you 
did measure bigger latencies and more compaction work, please post the 
numbers and details about the test.