Messages in this thread | | | Subject | Re: [PATCH 23/28] mm, page_alloc: Check multiple page fields with a single branch | From | Vlastimil Babka <> | Date | Tue, 26 Apr 2016 20:41:50 +0200 |
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On 04/15/2016 11:07 AM, Mel Gorman wrote: > Every page allocated or freed is checked for sanity to avoid corruptions > that are difficult to detect later. A bad page could be due to a number of > fields. Instead of using multiple branches, this patch combines multiple > fields into a single branch. A detailed check is only necessary if that > check fails. > > 4.6.0-rc2 4.6.0-rc2 > initonce-v1r20 multcheck-v1r20 > Min alloc-odr0-1 359.00 ( 0.00%) 348.00 ( 3.06%) > Min alloc-odr0-2 260.00 ( 0.00%) 254.00 ( 2.31%) > Min alloc-odr0-4 214.00 ( 0.00%) 213.00 ( 0.47%) > Min alloc-odr0-8 186.00 ( 0.00%) 186.00 ( 0.00%) > Min alloc-odr0-16 173.00 ( 0.00%) 173.00 ( 0.00%) > Min alloc-odr0-32 165.00 ( 0.00%) 166.00 ( -0.61%) > Min alloc-odr0-64 162.00 ( 0.00%) 162.00 ( 0.00%) > Min alloc-odr0-128 161.00 ( 0.00%) 160.00 ( 0.62%) > Min alloc-odr0-256 170.00 ( 0.00%) 169.00 ( 0.59%) > Min alloc-odr0-512 181.00 ( 0.00%) 180.00 ( 0.55%) > Min alloc-odr0-1024 190.00 ( 0.00%) 188.00 ( 1.05%) > Min alloc-odr0-2048 196.00 ( 0.00%) 194.00 ( 1.02%) > Min alloc-odr0-4096 202.00 ( 0.00%) 199.00 ( 1.49%) > Min alloc-odr0-8192 205.00 ( 0.00%) 202.00 ( 1.46%) > Min alloc-odr0-16384 205.00 ( 0.00%) 203.00 ( 0.98%) > > Again, the benefit is marginal but avoiding excessive branches is > important. Ideally the paths would not have to check these conditions at > all but regrettably abandoning the tests would make use-after-free bugs > much harder to detect. > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
I wonder, would it be just too ugly to add +1 to atomic_read(&page->_mapcount) and OR it with the rest for a truly single branch?
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