Re: [PATCH] mm: memcontrol: Make the walk_page_range() limit obvious

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Wed, Aug 31, 2016 at 05:17:30PM +0200, Michal Hocko wrote:
> On Wed 31-08-16 16:04:57, James Morse wrote:
> > Trying to walk all of virtual memory requires architecture specific
> > knowledge. On x86_64, addresses must be sign extended from bit 48,
> > whereas on arm64 the top VA_BITS of address space have their own set
> > of page tables.
> > 
> > mem_cgroup_count_precharge() and mem_cgroup_move_charge() both call
> > walk_page_range() on the range 0 to ~0UL, neither provide a pte_hole
> > callback, which causes the current implementation to skip non-vma regions.
> > 
> > As this call only expects to walk user address space, make it walk
> > 0 to  'highest_vm_end'.
> > 
> > Signed-off-by: James Morse <james.morse@arm.com>
> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > ---
> > This is in preparation for a RFC series that allows walk_page_range() to
> > walk kernel page tables too.
> 
> OK, so do I get it right that this is only needed with that change?
> Because AFAICS walk_page_range will be bound to the last vma->vm_end
> right now.

I think this is correct, find_vma() in walk_page_range() does that.

> If this is the case this should be mentioned in the changelog
> because the above might confuse somebody to think this is a bug fix.
> 
> Other than that this seams reasonable to me.

I'm fine with this change.

Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
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