From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
To: Xishi Qiu <qiuxishi@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
"'Kirill A . Shutemov'" <kirill.shutemov@linux.intel.com>,
Taku Izumi <izumi.taku@jp.fujitsu.com>,
Yisheng Xie <xieyisheng1@huawei.com>,
Linux MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC][PATCH] mm: merge as soon as possible when pcp alloc/free
Date: Mon, 7 Nov 2016 10:20:50 +0530 [thread overview]
Message-ID: <5820082A.9080906@linux.vnet.ibm.com> (raw)
In-Reply-To: <581FDD53.20804@huawei.com>
On 11/07/2016 07:18 AM, Xishi Qiu wrote:
> On 2016/11/5 20:29, Anshuman Khandual wrote:
>
>> On 11/05/2016 01:27 PM, Xishi Qiu wrote:
>>> Usually the memory of android phones is very small, so after a long
>>> running, the fragment is very large. Kernel stack which called by
>>> alloc_thread_stack_node() usually alloc 16K memory, and it failed
>>> frequently.
>>>
>>> However we have CONFIG_VMAP_STACK now, but it do not support arm64,
>>> and maybe it has some regression because of vmalloc, it need to
>>> find an area and create page table dynamically, this will take a short
>>> time.
>>>
>>> I think we can merge as soon as possible when pcp alloc/free to reduce
>>> fragment. The pcp page is hot page, so free it will cause cache miss,
>>> I use perf to test it, but it seems the regression is not so much, maybe
>>> it need to test more. Any reply is welcome.
>>
>> The idea of PCP is to have a fast allocation mechanism which does not depend
>> on an interrupt safe spin lock for every allocation. I am not very familiar
>> with this part of code but the following documentation from Mel Gorman kind
>> of explains that the this type of fragmentation problem which you might be
>> observing as one of the limitations of PCP mechanism.
>>
>> https://www.kernel.org/doc/gorman/html/understand/understand009.html
>> "Per CPU page list" sub header.
>>
>
> "The last potential problem is that buddies of newly freed pages could exist
> in other pagesets leading to possible fragmentation problems."
> So we should not change it, and this is a known issue, right?
Seems like that.
next prev parent reply other threads:[~2016-11-07 4:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-05 7:57 [RFC][PATCH] mm: merge as soon as possible when pcp alloc/free Xishi Qiu
2016-11-05 12:29 ` Anshuman Khandual
2016-11-07 1:48 ` Xishi Qiu
2016-11-07 4:50 ` Anshuman Khandual [this message]
2016-11-07 23:45 ` Andrew Morton
2016-11-08 11:03 ` Mel Gorman
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