Messages in this thread | | | Date | Tue, 22 Dec 2015 14:05:06 -0800 (PST) | From | David Rientjes <> | Subject | Re: [PATCH 1/2] mm/compaction: fix invalid free_pfn and compact_cached_free_pfn |
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On Mon, 21 Dec 2015, Joonsoo Kim wrote:
> free_pfn and compact_cached_free_pfn are the pointer that remember > restart position of freepage scanner. When they are reset or invalid, > we set them to zone_end_pfn because freepage scanner works in reverse > direction. But, because zone range is defined as [zone_start_pfn, > zone_end_pfn), zone_end_pfn is invalid to access. Therefore, we should > not store it to free_pfn and compact_cached_free_pfn. Instead, we need > to store zone_end_pfn - 1 to them. There is one more thing we should > consider. Freepage scanner scan reversely by pageblock unit. If free_pfn > and compact_cached_free_pfn are set to middle of pageblock, it regards > that sitiation as that it already scans front part of pageblock so we > lose opportunity to scan there. To fix-up, this patch do round_down() > to guarantee that reset position will be pageblock aligned. > > Note that thanks to the current pageblock_pfn_to_page() implementation, > actual access to zone_end_pfn doesn't happen until now. But, following > patch will change pageblock_pfn_to_page() so this patch is needed > from now on. > > Acked-by: Vlastimil Babka <vbabka@suse.cz> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: David Rientjes <rientjes@google.com>
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