Messages in this thread | | | Date | Fri, 13 Jan 2006 20:13:35 +0200 | From | Mika Penttilä <> | Subject | Re: [PATCH] BUG: gfp_zone() not mapping zone modifiers correctly and bad ordering of fallback lists |
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Mel Gorman wrote:
>Hi Andrew, > >This patch is divided into two parts and addresses a bug in how zone >fallback lists are calculated and how __GFP_* zone modifiers are mapped to >their equivilant ZONE_* type. It applies to 2.6.15-mm3 and has been tested >on x86 and ppc64. It has been reported by Yasunori Goto that it boots on >ia64. Details as follows; > >build_zonelists() attempts to be smart, and uses highest_zone() so that it >doesn't attempt to call build_zonelists_node() for empty zones. However, >build_zonelists_node() is smart enough to do the right thing by itself and >build_zonelists() already has the zone index that highest_zone() is meant >to provide. So, remove the unnecessary function highest_zone(). > >The helper function gfp_zone() assumes that the bits used in the zone modifier >of a GFP flag maps directory on to their ZONE_* equivalent and just applies a >mask. However, the bits do not map directly and the wrong fallback lists can >be used. If unluckly, the system can go OOM when plenty of suitable memory >is available. This patch redefines the __GFP_ zone modifier flags to allow >a simple mapping to their equivilant ZONE_ type. > > > What's the exact failure case? Afaik, we loop though all the GFP_ZONETYPES, building the appropriate zone lists at 0 - GFP_ZONETYPES-1 indexes. So the direct GFP -> ZONE mapping should do the right thing.
--Mika
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