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@xxxxxxxxxxxxx> 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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