Re: [RFC v2][PATCH]page_fault retry with NOPAGE_RETRY
From: Ying Han
Date: Sun Dec 07 2008 - 20:44:00 EST
Thanks Török for your experiment and that sounds great !
--Ying
On Sat, Dec 6, 2008 at 1:55 AM, Török Edwin <edwintorok@xxxxxxxxx> wrote:
> On 2008-12-06 11:52, Török Edwin wrote:
>> On 2008-12-05 21:40, Ying Han wrote:
>>
>>> changelog[v2]:
>>> - reduce the runtime overhead by extending the 'write' flag of
>>> handle_mm_fault() to indicate the retry hint.
>>> - add another two branches in filemap_fault with retry logic.
>>> - replace find_lock_page with find_lock_page_retry to make the code
>>> cleaner.
>>>
>>> todo:
>>> - there is potential a starvation hole with the retry. By the time the
>>> retry returns, the pages might be released. we can make change by holding
>>> page reference as well as remembering what the page "was"(in case the
>>> file was truncated). any suggestion here are welcomed.
>>>
>>> I also made patches for all other arch. I am posting x86_64 here first and
>>> i will post others by the time everyone feels comfortable of this patch.
>>>
>>> Edwin, please test this patch with your testcase and check if you get any
>>> performance improvement of mmap over read. I added another two more places
>>> in filemap_fault with retry logic which you might hit in your privous
>>> experiment.
>>>
>>>
>>
>> I get much better results with this patch than with v1, thanks!
>>
>> mmap now scales almost as well as read does (there is a small ~5%
>> overhead), which is a significant improvement over not scaling at all!
>>
>> Here are the results when running my testcase:
>>
>> Number of threads ->, 1,,, 2,,, 4,,, 8,,, 16
>> Kernel version, read, mmap, mixed, read, mmap, mixed, read, mmap, mixed,
>> read, mmap, mixed, read, mmap, mixed
>> 2.6.28-rc7-tip, 27.55, 26.18, 27.06, 16.18, 16.97, 16.10, 11.06, 11.64,
>> 11.41, 9.38, 9.97, 9.31, 9.37, 9.82, 9.3
>>
>>
>> Here are the /proc/lock_stat output when running my testcase, contention
>> is lower (34911+10462 vs 58590+7231), and waittime-total is better
>> (57 601 464 vs 234 170 024)
>>
>> lock_stat version 0.3
>> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>> class name con-bounces contentions
>> waittime-min waittime-max waittime-total acq-bounces
>> acquisitions holdtime-min holdtime-max holdtime-total
>> ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>> &mm->mmap_sem-W: 5843
>> 10462 2.89 138824.72 14217159.52
>> 18965 84205 1.81 5031.07 725293.65
>> &mm->mmap_sem-R: 20208
>> 34911 4.87 136797.26 57601464.49 55797
>> 1110394 1.89 164918.52 30551371.71
>> ---------------
>> &mm->mmap_sem 5341
>> [<ffffffff802bf9d7>] sys_munmap+0x47/0x80
>> &mm->mmap_sem 28579
>> [<ffffffff805d1c62>] do_page_fault+0x172/0xab0
>> &mm->mmap_sem 5030
>> [<ffffffff80211161>] sys_mmap+0xf1/0x140
>> &mm->mmap_sem 6331
>> [<ffffffff802a675e>] find_lock_page_retry+0xde/0xf0
>> ---------------
>> &mm->mmap_sem 13558
>> [<ffffffff802a675e>] find_lock_page_retry+0xde/0xf0
>> &mm->mmap_sem 4694
>> [<ffffffff802bf9d7>] sys_munmap+0x47/0x80
>> &mm->mmap_sem 3681
>> [<ffffffff80211161>] sys_mmap+0xf1/0x140
>> &mm->mmap_sem 23374
>> [<ffffffff805d1c62>] do_page_fault+0x172/0xab0
>>
>>
>> On clamd:
>>
>> Here holdtime-total is better (1 493 154 + 2 395 987 vs 2 087 538 + 2
>> 514 673), and number of contentions on read
>> (458 052 vs 5851
>
> typo, should have been: 458 052 vs 585 119
>
>
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