From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Thelen Subject: [PATCH] memcg: fix multiple large threshold notifications Date: Sat, 31 Aug 2013 17:06:42 -0700 Message-ID: <1377994002-1857-1-git-send-email-gthelen@google.com> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=from:to:cc:subject:date:message-id; bh=tZLHD0rNc9u0+6T0vwKbMAH3YGEmdEy+WTVRhmDMHbU=; b=COkiXAQTAU4Y0d/F0z/InxnO1jmIVALCDCYzgmY3P+gyIrQbBjoZ9ZuwLD+pFiI2d/ E5ryNqbM24DMnuVY3TV7lMstiwSCeeAWS5SRmgAFFJh4qRJJRv6BpVBrSM/CZj1fgqTl JJfEfbH3kSnZVfcnn2tuvJ4ZJjzOSQbyLq5Bev3iaDj07KG64DOKQlxLVUnB6jaF8i0g MWNBdkag5B/6Ftw7H1TW0m8xptov+2MC7J6I/g6iIhav9OOd3yXZfJZFkRJpN/bRLSE5 fVe32zM4SzQmWHWLg0DV0b9RrTdzHZDxlwbpmH2nSSjnownehuckfc/TZQWNqFN7GaBV h+Yw== Sender: owner-linux-mm@kvack.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andrew Morton , Johannes Weiner , Michal Hocko , Balbir Singh , KAMEZAWA Hiroyuki Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Greg Thelen A memory cgroup with (1) multiple threshold notifications and (2) at least one threshold >=2G was not reliable. Specifically the notifications would either not fire or would not fire in the proper order. The __mem_cgroup_threshold() signaling logic depends on keeping 64 bit thresholds in sorted order. mem_cgroup_usage_register_event() sorts them with compare_thresholds(), which returns the difference of two 64 bit thresholds as an int. If the difference is positive but has bit[31] set, then sort() treats the difference as negative and breaks sort order. This fix compares the two arbitrary 64 bit thresholds returning the classic -1, 0, 1 result. The test below sets two notifications (at 0x1000 and 0x81001000): cd /sys/fs/cgroup/memory mkdir x for x in 4096 2164264960; do cgroup_event_listener x/memory.usage_in_bytes $x | sed "s/^/$x listener:/" & done echo $$ > x/cgroup.procs anon_leaker 500M v3.11-rc7 fails to signal the 4096 event listener: Leaking... Done leaking pages. Patched v3.11-rc7 properly notifies: Leaking... 4096 listener:2013:8:31:14:13:36 Done leaking pages. The fixed bug is old. It appears to date back to the introduction of memcg threshold notifications in v2.6.34-rc1-116-g2e72b6347c94 "memcg: implement memory thresholds" Signed-off-by: Greg Thelen --- mm/memcontrol.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0878ff7..aa44621 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5616,7 +5616,13 @@ static int compare_thresholds(const void *a, const void *b) const struct mem_cgroup_threshold *_a = a; const struct mem_cgroup_threshold *_b = b; - return _a->threshold - _b->threshold; + if (_a->threshold > _b->threshold) + return 1; + + if (_a->threshold < _b->threshold) + return -1; + + return 0; } static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg) -- 1.8.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org