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Message-ID: <20090519074925.GA690@localhost> Date: Tue, 19 May 2009 15:49:25 +0800 From: Wu Fengguang <fengguang.wu@...el.com> To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> Cc: Christoph Lameter <cl@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, Elladan <elladan@...imo.com>, Nick Piggin <npiggin@...e.de>, Johannes Weiner <hannes@...xchg.org>, Peter Zijlstra <peterz@...radead.org>, Rik van Riel <riel@...hat.com>, "tytso@....edu" <tytso@....edu>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "minchan.kim@...il.com" <minchan.kim@...il.com> Subject: Re: [PATCH 2/3] vmscan: make mapped executable pages the first class citizen On Tue, May 19, 2009 at 03:20:19PM +0800, KOSAKI Motohiro wrote: > > On Tue, May 19, 2009 at 12:41:38PM +0800, KOSAKI Motohiro wrote: > > > Hi > > > > > > Thanks for great works. > > > > > > > > > > SUMMARY > > > > ======= > > > > The patch decreases the number of major faults from 50 to 3 during 10% cache hot reads. > > > > > > > > > > > > SCENARIO > > > > ======== > > > > The test scenario is to do 100000 pread(size=110 pages, offset=(i*100) pages), > > > > where 10% of the pages will be activated: > > > > > > > > for i in `seq 0 100 10000000`; do echo $i 110; done > pattern-hot-10 > > > > iotrace.rb --load pattern-hot-10 --play /b/sparse > > > > > > > > > Which can I download iotrace.rb? > > > > > > > > > > and monitor /proc/vmstat during the time. The test box has 2G memory. > > > > > > > > > > > > ANALYZES > > > > ======== > > > > > > > > I carried out two runs on fresh booted console mode 2.6.29 with the VM_EXEC > > > > patch, and fetched the vmstat numbers on > > > > > > > > (1) begin: shortly after the big read IO starts; > > > > (2) end: just before the big read IO stops; > > > > (3) restore: the big read IO stops and the zsh working set restored > > > > > > > > nr_mapped nr_active_file nr_inactive_file pgmajfault pgdeactivate pgfree > > > > begin: 2481 2237 8694 630 0 574299 > > > > end: 275 231976 233914 633 776271 20933042 > > > > restore: 370 232154 234524 691 777183 20958453 > > > > > > > > begin: 2434 2237 8493 629 0 574195 > > > > end: 284 231970 233536 632 771918 20896129 > > > > restore: 399 232218 234789 690 774526 20957909 > > > > > > > > and another run on 2.6.30-rc4-mm with the VM_EXEC logic disabled: > > > > > > I don't think it is proper comparision. > > > you need either following comparision. otherwise we insert many guess into the analysis. > > > > > > - 2.6.29 with and without VM_EXEC patch > > > - 2.6.30-rc4-mm with and without VM_EXEC patch > > > > > > > > > > > > > > begin: 2479 2344 9659 210 0 579643 > > > > end: 284 232010 234142 260 772776 20917184 > > > > restore: 379 232159 234371 301 774888 20967849 > > > > > > > > The numbers show that > > > > > > > > - The startup pgmajfault of 2.6.30-rc4-mm is merely 1/3 that of 2.6.29. > > > > I'd attribute that improvement to the mmap readahead improvements :-) > > > > > > > > - The pgmajfault increment during the file copy is 633-630=3 vs 260-210=50. > > > > That's a huge improvement - which means with the VM_EXEC protection logic, > > > > active mmap pages is pretty safe even under partially cache hot streaming IO. > > > > > > > > - when active:inactive file lru size reaches 1:1, their scan rates is 1:20.8 > > > > under 10% cache hot IO. (computed with formula Dpgdeactivate:Dpgfree) > > > > That roughly means the active mmap pages get 20.8 more chances to get > > > > re-referenced to stay in memory. > > > > > > > > - The absolute nr_mapped drops considerably to 1/9 during the big IO, and the > > > > dropped pages are mostly inactive ones. The patch has almost no impact in > > > > this aspect, that means it won't unnecessarily increase memory pressure. > > > > (In contrast, your 20% mmap protection ratio will keep them all, and > > > > therefore eliminate the extra 41 major faults to restore working set > > > > of zsh etc.) > > > > More results on X desktop, kernel 2.6.30-rc4-mm: > > > > nr_mapped nr_active_file nr_inactive_file pgmajfault pgdeactivate pgfree > > > > VM_EXEC protection ON: > > begin: 9740 8920 64075 561 0 678360 > > end: 768 218254 220029 565 798953 21057006 > > restore: 857 218543 220987 606 799462 21075710 > > restore X: 2414 218560 225344 797 799462 21080795 > > > > VM_EXEC protection OFF: > > begin: 9368 5035 26389 554 0 633391 > > end: 770 218449 221230 661 646472 17832500 > > restore: 1113 218466 220978 710 649881 17905235 > > restore X: 2687 218650 225484 947 802700 21083584 > > > > The added "restore X" means after IO, switch back and forth between the urxvt > > and firefox windows to restore their working set. I cannot explain why the > > absolute nr_mapped grows larger at the end of VM_EXEC OFF case. Maybe it's > > because urxvt is the foreground window during the first run, and firefox is the > > foreground window during the second run? > > > > Like the console mode, the absolute nr_mapped drops considerably - to 1/13 of > > the original size - during the streaming IO. > > > > The delta of pgmajfault is 3 vs 107 during IO, or 236 vs 393 during the whole > > process. > > hmmm. > > about 100 page fault don't match Elladan's problem, I think. > perhaps We missed any addional reproduce condition? Elladan's case is not the point of this test. Elladan's IO is use-once, so probably not a caching problem at all. This test case is specifically devised to confirm whether this patch works as expected. Conclusion: it is. Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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