Messages in this thread | | | Date | Tue, 19 May 2009 21:28:28 +0900 | Subject | Re: [PATCH 2/3] vmscan: make mapped executable pages the first class citizen | From | KOSAKI Motohiro <> |
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Hi
2009/5/19 Wu Fengguang <fengguang.wu@intel.com>: > On Tue, May 19, 2009 at 04:06:35PM +0800, KOSAKI Motohiro wrote: >> > > > 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. >> >> Dejection ;-) >> >> The number should address the patch is useful or not. confirming as expected >> is not so great. > > OK, let's make the conclusion in this way: > > The changelog analyzed the possible beneficial situation, and this > test backs that theory with real numbers, ie: it successfully stops > major faults when the active file list is slowly scanned when there > are partially cache hot streaming IO. > > Another (amazing) finding of the test is, only around 1/10 mapped pages > are actively referenced in the absence of user activities. > > Shall we protect the remaining 9/10 inactive ones? This is a question ;-)
Unfortunately, I don't reproduce again. I don't apply your patch yet. but mapped ratio is reduced only very little.
I think smem can show which library evicted. Can you try it?
download: http://www.selenic.com/smem/ usage: ./smem -m -r --abbreviate
We can't decide 9/10 is important or not. we need know actual evicted file list.
Thanks.
> Or, shall we take the "protect active VM_EXEC mapped pages" approach, > or Christoph's "protect all mapped pages all time, unless they grow > too large" attitude? I still prefer the best effort VM_EXEC heuristics. > > 1) the partially cache hot streaming IO is far more likely to happen > on (file) servers. For them, evicting the 9/10 inactive mapped > pages over night should be acceptable for sysadms. > > 2) for use-once IO on desktop, we have Rik's active file list > protection heuristics, so nothing to worry at all. > > 3) for big working set small memory desktop, the active list will > still be scanned, in this situation, why not evict some of the > inactive mapped pages? If they have not been accessed for 1 minute, > they are not likely be the user focus, and the tight memory > constraint can only afford to cache the user focused working set. > > Does that make sense? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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