On Tue, Dec 20, 2016 at 02:43:12PM +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 <[email protected]>
Acked-by: Mel Gorman <[email protected]> -- Mel Gorman SUSE Labs
