From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx161.postini.com [74.125.245.161]) by kanga.kvack.org (Postfix) with SMTP id 238466B00EB for ; Fri, 27 Apr 2012 13:42:30 -0400 (EDT) Received: by laah2 with SMTP id h2so51228laa.2 for ; Fri, 27 Apr 2012 10:42:28 -0700 (PDT) From: Ying Han Subject: [PATCH 1/2] mm: Warn once when a page is freed with PG_mlocked Date: Fri, 27 Apr 2012 10:42:26 -0700 Message-Id: <1335548546-25040-1-git-send-email-yinghan@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko , Johannes Weiner , Mel Gorman , KAMEZAWA Hiroyuki , Rik van Riel , Minchan Kim , Hugh Dickins , KOSAKI Motohiro , Nick Piggin , Andrew Morton Cc: linux-mm@kvack.org, Mel Gorman I am resending this patch orginally from Mel, and the reason we spotted this is due to the next patch where I am adding the mlock stat into per-memcg meminfo. We found out that it is impossible to update the counter if the page is in the freeing patch w/ mlocked bit set. Then we started wondering if it is possible at all. It shouldn't happen that freeing a mlocked page without going through munlock_vma_pages_all(). Looks like it did happen few years ago, and here is the patch introduced it commit 985737cf2ea096ea946aed82c7484d40defc71a8 Author: Lee Schermerhorn Date: Sat Oct 18 20:26:53 2008 -0700 mlock: count attempts to free mlocked page There are two ways to persue and I would like to ask people's opinion: 1. revert the patch totally and the page will get into bad_page(). Then we get the report as well. 2. fix up the page like the patch does but put on warn_once() to report the problem. People might feel more confident by doing step by step which adding the warn_on() first and then revert it later. So I resend the patch from Mel and here is the patch: When a page is freed with the PG_mlocked set, it is considered an unexpected but recoverable situation. A counter records how often this event happens but it is easy to miss that this event has occured at all. This patch warns once when PG_mlocked is set to prompt debuggers to check the counter to see how often it is happening. Signed-off-by: Ying Han Signed-off-by: Mel Gorman Acked-by: Johannes Weiner --- mm/page_alloc.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index a712fb9..4f905af 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -599,6 +599,11 @@ out: */ static inline void free_page_mlock(struct page *page) { + WARN_ONCE(1, KERN_WARNING + "Page flag mlocked set for process %s at pfn:%05lx\n" + "page:%p flags:%#lx\n", + current->comm, page_to_pfn(page), + page, page->flags|__PG_MLOCKED); __dec_zone_page_state(page, NR_MLOCK); __count_vm_event(UNEVICTABLE_MLOCKFREED); } -- 1.7.7.3 -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org