Messages in this thread | | | From | Naoya Horiguchi <> | Subject | Re: [PATCH v1] tools/vm/page-types.c: remove memset() in walk_pfn() | Date | Tue, 8 Mar 2016 05:58:35 +0000 |
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On Tue, Mar 08, 2016 at 08:12:09AM +0300, Konstantin Khlebnikov wrote: > On Tue, Mar 8, 2016 at 4:47 AM, Naoya Horiguchi > <n-horiguchi@ah.jp.nec.com> wrote: > > I found that page-types is very slow and my testing shows many timeout errors. > > Here's an example with a simple program allocating 1000 thps. > > > > $ time ./page-types -p $(pgrep -f test_alloc) > > ... > > real 0m17.201s > > user 0m16.889s > > sys 0m0.312s > > > > $ time ./page-types.patched -p $(pgrep -f test_alloc) > > ... > > real 0m0.182s > > user 0m0.046s > > sys 0m0.135s > > > > Most of time is spent in memset(), which isn't necessary because we check > > that the return of kpagecgroup_read() is equal to pages and uninitialized > > memory is never used. So we can drop this memset(). > > These zeros are used in show_page_range() - for merging pages into ranges.
Hi Konstantin,
Thank you for the response. The below code does solve the problem, so that's fine.
But I don't understand how the zeros are used. show_page_range() is called via add_page() which is called for i=0 to i=pages-1, and the buffer cgi is already filled for the range [i, pages-1] by kpagecgroup_read(), so even if without zero initialization, kpagecgroup_read() properly fills zeros, right? IOW, is there any problem if we don't do this zero initialization?
Thanks, Naoya Horiguchi
> You could add fast-path for count=1 > > @@ -633,7 +633,10 @@ static void walk_pfn(unsigned long voffset, > unsigned long pages; > unsigned long i; > > - memset(cgi, 0, sizeof cgi); > + if (count == 1) > + cgi[0] = 0; > + else > + memset(cgi, 0, sizeof cgi); > > while (count) { > batch = min_t(unsigned long, count, KPAGEFLAGS_BATCH); >
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