Re: [RFC v2][PATCH]page_fault retry with NOPAGE_RETRY

[Ying Han <yinghan@google.com>]

Andrew, if it sounds good to include this patch in -mm at this point?

thanks

--Ying

On Sun, Dec 7, 2008 at 5:43 PM, Ying Han <yinghan@google.com> wrote:
> Thanks Torok for your experiment and that sounds great !
>
> --Ying
>
> On Sat, Dec 6, 2008 at 1:55 AM, Torok Edwin <edwintorok@gmail.com> wrote:
>> On 2008-12-06 11:52, Torok 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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