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

["Török Edwin" <edwintorok@gmail.com>]

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