Re: [PATCH 4/6] mm/vmalloc: make set_area_direct_map HUGE_VMAP friendly

> set_area_direct_map() always updates direct map alias permissions in
> single page increments.
> 
> For HUGE_VMAP areas it's suboptimal. Not only the loop in
> set_area_direct_map() needlessly has more iterations (e.g times 512 on
> x86), but it also causes fragmentation of the direct map that could be
> avoided for the HUGE_VMAP areas populated with large pages.
> 
> All pages in an area are always of the same order: either same-order
> large pages when VM_ALLOW_HUGE_VMAP is set and all huge pages were
> successfully allocated, or order-0 page when VM_ALLOW_HUGE_VMAP is
> cleared or when huge pages allocation fails and fallback path is taken.
> 
> Instead of updating the direct map permissions for every order-0 page in
> an area, use the area's page_order as the loop increment and update the
> large pages in one call to set_direct_map_{invalid,default}_noflush().
> 
> Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

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