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4422c04bbb
Align the start address and size of VRAM area to 2M as per comments from Russell King: > > So, why SZ_2M? > > Firstly, that's the granularity which we allocate page tables - one > Linux page table covers 2MB of memory. We want to avoid creating page > tables for the main memory mapping as that increases TLB pressure through > the use of additional TLB entries, and more page table walks. > > Plus, we never used to allow the kernel's direct memory mapping to be > mapped at anything less than section size - this restriction has since > been lifted due to OMAP SRAM problems, but I'd rather we stuck with it > to ensure that we have proper behaviour from all parts of the system. > > Secondly, we don't want to end up with lots of fragmentation at the end > of the memory mapping as that'll reduce performance, not only by making > the pfn_valid() search more expensive. > > Emsuring a minimum allocation size and alignment makes sure that the > regions can be coalesced together into one block, and minimises run-time > expenses. > > So please, 2MB, or if you object, at the _very_ _least_ 1MB. But > definitely not PAGE_SIZE. Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com> Acked-by: Tony Lindgren <tony@atomide.com> |
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