Re: [PATCH v1] tools/vm/page-types.c: remove memset() in walk_pfn()

[Konstantin Khlebnikov]

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.

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);


>
> Fixes: 954e95584579 ("tools/vm/page-types.c: add memory cgroup dumping and filtering")
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> ---
>  tools/vm/page-types.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git v4.5-rc5-mmotm-2016-02-24-16-18/tools/vm/page-types.c v4.5-rc5-mmotm-2016-02-24-16-18_patched/tools/vm/page-types.c
> index dab61c3..c192baf 100644
> --- v4.5-rc5-mmotm-2016-02-24-16-18/tools/vm/page-types.c
> +++ v4.5-rc5-mmotm-2016-02-24-16-18_patched/tools/vm/page-types.c
> @@ -633,8 +633,6 @@ static void walk_pfn(unsigned long voffset,
>         unsigned long pages;
>         unsigned long i;
>
> -       memset(cgi, 0, sizeof cgi);
> -
>         while (count) {
>                 batch = min_t(unsigned long, count, KPAGEFLAGS_BATCH);
>                 pages = kpageflags_read(buf, index, batch);
> --
> 2.7.0
>