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SubjectRe: [PATCH 1/2] thp: Add compound tail page _mapcount when mapped
On Fri, 25 Nov 2011 13:47:09 +0800
Youquan Song <youquan.song@intel.com> wrote:

> With 3.2-rc kernel, the IOMMU 2M page in KVM works. While I try to us IOMMU
> 1GB page in KVM, I encounter a oops and 1GB page total fail to be used.
> The root cause is that 1GB page allocation calls gup_huge_pud() while 2M
> page calls gup_huge_pmd. If compound pages are used and the page is tail page,
> gup_huge_pmd increase _mapcount to record tail page are mapped while
> gup_huge_pud does not include this process. So when the mapped page is relesed,
> it will result in kernel oops because the page does not mark mapped.
>
> This patch add tail process for compound page in 1GB huge page which keeps the
> same process as 2M page.
>
> Reproduce like:
> 1. Add grub boot option: hugepagesz=1G hugepages=8
> 2. mount -t hugetlbfs -o pagesize=1G hugetlbfs /dev/hugepages
> 3.qemu-kvm -m 2048 -hda os-kvm.img -cpu kvm64 -smp 4 -mem-path /dev/hugepages
> -net none -device pci-assign,host=07:00.1
>
> kernel BUG at mm/swap.c:114!
>
> ...
>
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -201,6 +201,8 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
> do {
> VM_BUG_ON(compound_head(page) != head);
> pages[*nr] = page;
> + if (PageTail(page))
> + get_huge_page_tail(page);
> (*nr)++;
> page++;
> refs++;

Is the patch also applicable to 3.1.x?


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