On Tue, 2016-12-20 at 14:43 +0100, Vlastimil Babka wrote: > The flag is rarely enabled or even changed, so it's an ideal static > key > candidate. Since it's being checked in the page allocator fastpath > via > gfpflags_to_migratetype(), it may actually save some valuable cycles. > > Here's a diff excerpt from __alloc_pages_nodemask() assembly: > > -movl page_group_by_mobility_disabled(%rip), %ecx > +.byte 0x0f,0x1f,0x44,0x00,0 > movl %r9d, %eax > shrl $3, %eax > andl $3, %eax > -testl %ecx, %ecx > -movl $0, %ecx > -cmovne %ecx, %eax > > I.e. a NOP instead of test, conditional move and some assisting > moves. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Rik van Riel <riel@xxxxxxxxxx> -- All Rights Reversed.
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