From: Wanlong G. <gao...@cn...> - 2012-07-10 00:26:16
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On 07/09/2012 11:51 PM, Zhouping Liu wrote: > > > ----- Original Message ----- >> From: "Caspar Zhang" <ca...@ca...> >> To: gao...@cn... >> Cc: "Zhouping Liu" <zl...@re...>, "LTP list" sourceforge.net> >> Sent: Monday, July 9, 2012 10:15:17 PM >> Subject: Re: [LTP] [PATCH 2/2] mm/lib: increase sleep time in ksm scanning >> >> On 07/09/2012 09:10 PM, Wanlong Gao wrote: >>> On 07/09/2012 08:37 PM, Caspar Zhang wrote: >>>> On 07/09/2012 07:32 PM, Wanlong Gao wrote: >>>>> On 07/09/2012 05:51 PM, Caspar Zhang wrote: >>>>>> >>>>>> for some systems under pressure, we've observed that sleeping 5 >>>>>> seconds is not sufficient for completing ksm scanning, to fix >>>>>> this, we should give ksmd more time to scan the mergable pages >>>>>> by increasing sleeping time to 10s. >>>>> >>>>> If 5s is not enough, isn't we waiting here already? >>>> >>>> Sorry, I'm not catching you... :-( the problem currently we >>>> encounter is that if 5s given, all ksm values (pages_sharing, >>>> pages_shared, etc) might remain the same between before and after >>>> sleeping, so the wait_ksmd function could exit. But in fact the >>>> kernel could be busy under pressure and it just needs more than 5s >>>> to merge the same page. Using 10s as polling interval can make >>>> sure >>>> if ksm values remains the same between each loop, it should >>>> indicates that ksmd has done scanning correctly. >>>> >>> >>> Oops, it's a serious problem, so can we first wait for changing and >>> then wait for not changing? I'm afraid that hard coded sleep time >>> can't do the right thing on some systems. >> >> IMO the current implementation does the same thing as you suggested. >> We >> wait for certain interval (5s for now, 10s proposed), and check if >> ksm >> values increased, if still changing, continue next sleep interval. >> Adding a "wait-for-not-changing" in fact has the same effect as >> increasing the original sleep time. >> >> theoretically, sleeping interval should be as larger as possible, but >> it >> will cost unnecessary running time if the interval is set too big in >> the >> this case. I'd say 10s is a "for-now-best-practice" during my several >> running (both w/ and w/o pressure). Besides, I'm not sure how ksm >> developers think of current ksm performance, but I think if ksmd >> takes >> more than 10s to merge two same pages, it will be a big performance >> issue. > > yes, I think so. > > and 5s interval is enough, I tested it on several low-memory/dull systems > during composing the patch, it's all OK. > But in order to cover more different systems, IMO, I also proposed 10s, > and it shouldn't be more bigger, or it will be a defect of ksm performance. Ok, no objection. Reviewed-by: Wanlong Gao <gao...@cn...> > |