Messages in this thread |  | | Date | Sun, 23 Mar 2008 00:47:25 -0300 | From | "Carlos R. Mafra" <> | Subject | Re: 103 sec. latency: sync_page() with TASK_UNINTERRUPTIBLE (?) (bisected) |
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> Cause Maximum Percentage > sync_page __lock_page handle_mm_fault do_page_faul103659.0 msec 59.8 % > get_request_wait __make_request generic_make_reque1992.0 msec 10.2 % > get_request_wait __make_request generic_make_reque1620.7 msec 4.6 % > sync_page __lock_page find_lock_page filemap_fault399.3 msec 3.4 % > sync_buffer __wait_on_buffer __bread ext3_get_bran292.9 msec 1.3 % > sync_page __lock_page handle_mm_fault do_page_faul200.5 msec 0.3 % > Scheduler: waiting for cpu 155.9 msec 18.9 % > sync_page __lock_page handle_mm_fault do_page_faul117.5 msec 0.1 % > congestion_wait try_to_free_pages __alloc_pages re103.5 msec 0.2 % > r_code > > > Process X (2910) > sync_page __lock_page handle_mm_fault do_page_faul103659.0 msec 98.5 % > Scheduler: waiting for cpu 64.6 msec 1.3 % > sync_page __lock_page find_lock_page filemap_fault 51.4 msec 0.2 %lt do_page_fault error_code > sync_buffer __wait_on_buffer __bread ext3_get_bran 17.8 msec 0.0 % ext3_get_block do_mpage_readpage mpage_readpa > sync_page __lock_page handle_mm_fault do_page_faul 9.1 msec 0.0 %ig ault > > The experience goes like this: > > 1) Boot with 2.6.25-rc6-00243-g028011e > 2) Log into X > 3) Open a 380MB file with xjed > > It takes more than 6 minutes to load the file, and meanwhile > I experience very bad desktop interactivity (like 1 minute to > the result of pressing F12 in Window Maker to appear in the > screen). > > If, after step 2), I start using firefox, thunderbird, play some > music etc and then close all these apps and go to step 3), > the loading finishes in about 2 minutes (and I have very > good interactivity meanwhile). > > So I noticed that when xjed is opening the file it is in > 'D' state (reported by ps), and while greping the kernel > source code for 'sync_page' I've found this comment > in mm/filemap.c: > > /** > * __lock_page - get a lock on the page, assuming we need to sleep to get it > * @page: the page to lock > * > * Ugly. Running sync_page() in state TASK_UNINTERRUPTIBLE is scary. If some > * random driver's requestfn sets TASK_RUNNING, we could busywait. However > * chances are that on the second loop, the block layer's plug list is empty, > * so sync_page() will then return in state TASK_UNINTERRUPTIBLE. > */ > > "Ugly. Running sync_page() in state TASK_UNINTERRUPTIBLE is scary." > > It appears that my problem with xjed in 'D' state while loading, > and sync_page() appearing in latencytop with 103 secs of latency > may be related through the "ugliness" described above. > > So I was wondering if there is a way to fix this. Note that > this issue does not happen if I load the file after using the > computer for a while, so it is not impossible to have good > interactivity while loading that big file.
After lots of tests, it turned out to be a regression from 2.6.24.
I bisected it down to f1a9ee758de7de1e040de849fdef46e6802ea117 ("kswapd should only wait on IO if there is IO").
If a revert the above commit from the latest git kernel (v2.6.25-rc6-243-g028011e), then I get an very good interactivity while xjed is loading the 380MB file (meaning that I can do other things during the load). Otherwise it takes almost 3 times longer to load, and interactivity is very bad in the meanwhile. I doubled checked it.
I hope this information will be useful, and I can try any patches if necessary.
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