tools/vm/page-types.c: avoid memset() in walk_pfn() when count == 1
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
Most of time is spent in memset(). Currently memset() clears over whole
buffer for every walk_pfn() call, which is inefficient when walk_pfn()
is called from walk_vma(), because in that case walk_pfn() is called for
each pfn. So this patch limits the zero initialization only for the
first element.
$ time ./page-types.patched -p $(pgrep -f test_alloc)
...
real 0m0.182s
user 0m0.046s
sys 0m0.135s
Fixes: 954e95584579 ("tools/vm/page-types.c: add memory cgroup dumping and filtering")
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Suggested-by: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index dab61c3..e92903f 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -633,7 +633,15 @@
unsigned long pages;
unsigned long i;
- memset(cgi, 0, sizeof cgi);
+ /*
+ * kpagecgroup_read() reads only if kpagecgroup were opened, but
+ * /proc/kpagecgroup might even not exist, so it's better to fill
+ * them with zeros here.
+ */
+ if (count == 1)
+ cgi[0] = 0;
+ else
+ memset(cgi, 0, sizeof cgi);
while (count) {
batch = min_t(unsigned long, count, KPAGEFLAGS_BATCH);