Messages in this thread Patch in this message | | | Date | Sat, 06 Dec 2008 11:52:08 +0200 | From | Török Edwin <> | Subject | Re: [RFC v2][PATCH]page_fault retry with NOPAGE_RETRY |
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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
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: 346769 533541 1.62 99819.40 454843342.63 411259 588486 1.33 6719.62 2395987.75 &mm->mmap_sem-R: 197856 458052 1.59 99800.28 313508721.01 338158 653427 1.71 25421.10 1493154.95 --------------- &mm->mmap_sem 427857 [<ffffffff805d1c62>] do_page_fault+0x172/0xab0 &mm->mmap_sem 266464 [<ffffffff802bf9d7>] sys_munmap+0x47/0x80 &mm->mmap_sem 251689 [<ffffffff802110d6>] sys_mmap+0x66/0x140 &mm->mmap_sem 15187 [<ffffffff80211161>] sys_mmap+0xf1/0x140 --------------- &mm->mmap_sem 226908 [<ffffffff802110d6>] sys_mmap+0x66/0x140 &mm->mmap_sem 483909 [<ffffffff805d1c62>] do_page_fault+0x172/0xab0 &mm->mmap_sem 229404 [<ffffffff802bf9d7>] sys_munmap+0x47/0x80 &mm->mmap_sem 13229 [<ffffffff80211161>] sys_mmap+0xf1/0x140
...............................................................................................................................................................................................
&sem->wait_lock: 112617 114394 0.41 111.20 225590.14 1517470 6300681 0.27 4103.77 3814684.55 --------------- &sem->wait_lock 5634 [<ffffffff8043a608>] __up_write+0x28/0x170 &sem->wait_lock 13595 [<ffffffff805ce4dc>] __down_read+0x1c/0xbc &sem->wait_lock 38882 [<ffffffff8043a4a0>] __down_read_trylock+0x20/0x60 &sem->wait_lock 30718 [<ffffffff8043a773>] __up_read+0x23/0xc0 --------------- &sem->wait_lock 21389 [<ffffffff8043a4a0>] __down_read_trylock+0x20/0x60 &sem->wait_lock 48959 [<ffffffff8043a608>] __up_write+0x28/0x170 &sem->wait_lock 24330 [<ffffffff8043a773>] __up_read+0x23/0xc0 &sem->wait_lock 9000 [<ffffffff805ce4dc>] __down_read+0x1c/0xbc
> @@ -694,6 +694,7 @@ static inline int page_mapped(struct page *page) > #define VM_FAULT_SIGBUS 0x0002 > #define VM_FAULT_MAJOR 0x0004 > #define VM_FAULT_WRITE 0x0008 /* Special case for get_user_pages */ > +#define VM_FAULT_RETRY 0x0010 > > #define VM_FAULT_NOPAGE 0x0100 /* ->fault installed the pte, not return page >
The patch got damaged here, and failed to apply, I added the missing */, and then git-am -3 applied it.
Best regards, --Edwin
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