Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762240Ab3ECAG5 (ORCPT ); Thu, 2 May 2013 20:06:57 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:55334 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932808Ab3ECABs (ORCPT ); Thu, 2 May 2013 20:01:48 -0400 From: Cody P Schafer To: Linux MM Cc: LKML , Cody P Schafer , Simon Jeons Subject: [RFC PATCH v3 28/31] mm/page_alloc: in page_outside_zone_boundaries(), avoid premature decisions. Date: Thu, 2 May 2013 17:01:00 -0700 Message-Id: <1367539263-19999-29-git-send-email-cody@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.2.2 In-Reply-To: <1367539263-19999-1-git-send-email-cody@linux.vnet.ibm.com> References: <1367539263-19999-1-git-send-email-cody@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13050300-7182-0000-0000-00000684BA0C Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1938 Lines: 50 With some code that expands the zone boundaries, VM_BUG_ON(bad_range()) was being triggered. Previously, page_outside_zone_boundaries() decided that once it detected a page outside the boundaries, it was certainly outside even if the seqlock indicated the data was invalid & needed to be reread. This methodology _almost_ works because zones are only ever grown. However, becase the zone span is stored as a start and a length, some expantions momentarily appear as shifts to the left (when the zone_start_pfn is assigned prior to zone_spanned_pages). If we want to remove the seqlock around zone_start_pfn & zone spanned_pages, always writing the spanned_pages first, issuing a memory barrier, and then writing the new zone_start_pfn _may_ work. The concern there is that we could be seen as shrinking the span when zone_start_pfn is written (the entire span would shift to the left). As there will be no pages in the exsess span that actually belong to the zone being manipulated, I don't expect there to be issues. Signed-off-by: Cody P Schafer --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 879ab9d..3695ca5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -239,12 +239,13 @@ bool oom_killer_disabled __read_mostly; #ifdef CONFIG_DEBUG_VM static int page_outside_zone_boundaries(struct zone *zone, struct page *page) { - int ret = 0; + int ret; unsigned seq; unsigned long pfn = page_to_pfn(page); unsigned long sp, start_pfn; do { + ret = 0; seq = zone_span_seqbegin(zone); start_pfn = zone->zone_start_pfn; sp = zone->spanned_pages; -- 1.8.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/