Re: [Qemu-devel] [PATCH] mm: hugetlb: initialize PG_reserved for tail pages of gigantig compound pages

[Rik van Riel <riel@redhat.com>]

On 10/10/2013 12:12 PM, Andrea Arcangeli wrote:
> 11feeb498086a3a5907b8148bdf1786a9b18fc55 introduced a memory leak when
> KVM is run on gigantic compound pages.
>
> 11feeb498086a3a5907b8148bdf1786a9b18fc55 depends on the assumption
> that PG_reserved is identical for all head and tail pages of a
> compound page. So that if get_user_pages returns a tail page, we don't
> need to check the head page in order to know if we deal with a
> reserved page that requires different refcounting.
>
> The assumption that PG_reserved is the same for head and tail pages is
> certainly correct for THP and regular hugepages, but gigantic
> hugepages allocated through bootmem don't clear the PG_reserved on the
> tail pages (the clearing of PG_reserved is done later only if the
> gigantic hugepage is freed).
>
> This patch corrects the gigantic compound page initialization so that
> we can retain the optimization in
> 11feeb498086a3a5907b8148bdf1786a9b18fc55. The cacheline was already
> modified in order to set PG_tail so this won't affect the boot time of
> large memory systems.
>
> Reported-by: andy123 <ajs124.ajs124@gmail.com>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>

Acked-by: Rik van Riel <riel@redhat.com>