linux-kernel - [PATCH v1] tools/vm/page-types.c: remove memset() in walk

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Date:	Tue,  8 Mar 2016 10:47:32 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	linux-mm@...ck.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vladimir Davydov <vdavydov@...tuozzo.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-kernel@...r.kernel.org,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: [PATCH v1] tools/vm/page-types.c: remove memset() in walk_pfn()

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().

Fixes: 954e95584579 ("tools/vm/page-types.c: add memory cgroup dumping and filtering")
Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
---
 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