From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <447DCF5A.7020407@shadowen.org> Date: Wed, 31 May 2006 18:16:10 +0100 From: Andy Whitcroft MIME-Version: 1.0 Subject: Re: [stable] [PATCH 0/2] Zone boundary alignment fixes, default configuration References: <447173EF.9090000@shadowen.org> <20060531001322.GJ18769@moss.sous-sol.org> In-Reply-To: <20060531001322.GJ18769@moss.sous-sol.org> Content-Type: multipart/mixed; boundary="------------070903070307020504090409" Sender: owner-linux-mm@kvack.org Return-Path: To: Chris Wright Cc: Andrew Morton , Mel Gorman , Nick Piggin , stable@kernel.org, Linux Memory Management List-ID: This is a multi-part message in MIME format. --------------070903070307020504090409 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Chris Wright wrote: > * Andy Whitcroft (apw@shadowen.org) wrote: > >>I think a concensus is forming that the checks for merging across >>zones were removed from the buddy allocator without anyone noticing. >>So I propose that the configuration option UNALIGNED_ZONE_BOUNDARIES >>default to on, and those architectures which have been auditied >>for alignment may turn it off. > > > So what's the final outcome here for -stable? The only > relevant patch upstream appears to be Bob Picco's patch > I am not sure we necessarily need to make any changes for stable. The lack of alignment checks has been in the mainline tree for a number of months. I believe that i386 in the simple cases should be aligned correctly and that covers the majority of users. If we are going to make any changes then I'd say we want two patches. The node_mem_map alignment patch from Bob Picco (as cited above) and the attached patch. This is a simplification of the patches currently in -mm, it should be functionally equivalent to the changes in -mm without the exclusions and configuration options. I've just run a regression suite over this one on the machines I have here without any problems. Comments? -apw --------------070903070307020504090409 Content-Type: text/plain; name="zone-allow-unaligned-zone-boundaries-for-2616-stable" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="zone-allow-unaligned-zone-boundaries-for-2616-stable" From: Andy Whitcroft [Minimal fix for unaligned zone boundaries for stable.] The buddy allocator has a requirement that boundaries between contigious zones occur aligned with the the MAX_ORDER ranges. Where they do not we will incorrectly merge pages cross zone boundaries. This can lead to pages from the wrong zone being handed out. Originally the buddy allocator would check that buddies were in the same zone by referencing the zone start and end page frame numbers. This was removed as it became very expensive and the buddy allocator already made the assumption that zones boundaries were aligned. It is clear that not all configurations and architectures are honouring this alignment requirement. Therefore it seems safest to reintroduce support for non-aligned zone boundaries. This patch introduces a new check when considering a page a buddy it compares the zone_table index for the two pages and refuses to merge the pages where they do not match. The zone_table index is unique for each node/zone combination when FLATMEM/DISCONTIGMEM is enabled and for each section/zone combination when SPARSEMEM is enabled (a SPARSEMEM section is at least a MAX_ORDER size). Signed-off-by: Andy Whitcroft --- include/linux/mm.h | 7 +++++-- mm/page_alloc.c | 17 +++++++++++------ 2 files changed, 16 insertions(+), 8 deletions(-) diff -upN reference/include/linux/mm.h current/include/linux/mm.h --- reference/include/linux/mm.h +++ current/include/linux/mm.h @@ -464,10 +464,13 @@ static inline unsigned long page_zonenum struct zone; extern struct zone *zone_table[]; +static inline int page_zone_id(struct page *page) +{ + return (page->flags >> ZONETABLE_PGSHIFT) & ZONETABLE_MASK; +} static inline struct zone *page_zone(struct page *page) { - return zone_table[(page->flags >> ZONETABLE_PGSHIFT) & - ZONETABLE_MASK]; + return zone_table[page_zone_id(page)]; } static inline unsigned long page_to_nid(struct page *page) diff -upN reference/mm/page_alloc.c current/mm/page_alloc.c --- reference/mm/page_alloc.c +++ current/mm/page_alloc.c @@ -270,22 +270,27 @@ __find_combined_index(unsigned long page * we can do coalesce a page and its buddy if * (a) the buddy is not in a hole && * (b) the buddy is in the buddy system && - * (c) a page and its buddy have the same order. + * (c) a page and its buddy have the same order && + * (d) a page and its buddy are in the same zone. * * For recording whether a page is in the buddy system, we use PG_buddy. * Setting, clearing, and testing PG_buddy is serialized by zone->lock. * * For recording page's order, we use page_private(page). */ -static inline int page_is_buddy(struct page *page, int order) +static inline int page_is_buddy(struct page *page, struct page *buddy, + int order) { #ifdef CONFIG_HOLES_IN_ZONE - if (!pfn_valid(page_to_pfn(page))) + if (!pfn_valid(page_to_pfn(buddy))) return 0; #endif - if (PageBuddy(page) && page_order(page) == order) { - BUG_ON(page_count(page) != 0); + if (page_zone_id(page) != page_zone_id(buddy)) + return 0; + + if (PageBuddy(buddy) && page_order(buddy) == order) { + BUG_ON(page_count(buddy) != 0); return 1; } return 0; @@ -336,7 +341,7 @@ static inline void __free_one_page(struc struct page *buddy; buddy = __page_find_buddy(page, page_idx, order); - if (!page_is_buddy(buddy, order)) + if (!page_is_buddy(page, buddy, order)) break; /* Move the buddy up one level. */ list_del(&buddy->lru); --------------070903070307020504090409-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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