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Date: Sun, 11 Aug 2013 23:21:46 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc: Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Andi Kleen <andi@...stfloor.org>,
Hillf Danton <dhillf@...il.com>, Michal Hocko <mhocko@...e.cz>,
Rik van Riel <riel@...hat.com>,
Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org,
Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH 8/9] migrate: check movability of hugepage in unmap_and_move_huge_page()
Naoya Horiguchi <n-horiguchi@...jp.nec.com> writes:
> Currently hugepage migration works well only for pmd-based hugepages
> (mainly due to lack of testing,) so we had better not enable migration
> of other levels of hugepages until we are ready for it.
>
> Some users of hugepage migration (mbind, move_pages, and migrate_pages)
> do page table walk and check pud/pmd_huge() there, so they are safe.
> But the other users (softoffline and memory hotremove) don't do this,
> so without this patch they can try to migrate unexpected types of hugepages.
>
> To prevent this, we introduce hugepage_migration_support() as an architecture
> dependent check of whether hugepage are implemented on a pmd basis or not.
> And on some architecture multiple sizes of hugepages are available, so
> hugepage_migration_support() also checks hugepage size.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
> arch/arm/mm/hugetlbpage.c | 5 +++++
> arch/arm64/mm/hugetlbpage.c | 5 +++++
> arch/ia64/mm/hugetlbpage.c | 5 +++++
> arch/metag/mm/hugetlbpage.c | 5 +++++
> arch/mips/mm/hugetlbpage.c | 5 +++++
> arch/powerpc/mm/hugetlbpage.c | 10 ++++++++++
> arch/s390/mm/hugetlbpage.c | 5 +++++
> arch/sh/mm/hugetlbpage.c | 5 +++++
> arch/sparc/mm/hugetlbpage.c | 5 +++++
> arch/tile/mm/hugetlbpage.c | 5 +++++
> arch/x86/mm/hugetlbpage.c | 8 ++++++++
> include/linux/hugetlb.h | 12 ++++++++++++
> mm/migrate.c | 10 ++++++++++
> 13 files changed, 85 insertions(+)
>
> diff --git v3.11-rc3.orig/arch/arm/mm/hugetlbpage.c v3.11-rc3/arch/arm/mm/hugetlbpage.c
> index 3d1e4a2..3f3b6a7 100644
> --- v3.11-rc3.orig/arch/arm/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/arm/mm/hugetlbpage.c
> @@ -99,3 +99,8 @@ int pmd_huge(pmd_t pmd)
> {
> return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
> }
> +
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> diff --git v3.11-rc3.orig/arch/arm64/mm/hugetlbpage.c v3.11-rc3/arch/arm64/mm/hugetlbpage.c
> index 2fc8258..5e9aec3 100644
> --- v3.11-rc3.orig/arch/arm64/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/arm64/mm/hugetlbpage.c
> @@ -54,6 +54,11 @@ int pud_huge(pud_t pud)
> return !(pud_val(pud) & PUD_TABLE_BIT);
> }
>
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> +
> static __init int setup_hugepagesz(char *opt)
> {
> unsigned long ps = memparse(opt, &opt);
> diff --git v3.11-rc3.orig/arch/ia64/mm/hugetlbpage.c v3.11-rc3/arch/ia64/mm/hugetlbpage.c
> index 76069c1..68232db 100644
> --- v3.11-rc3.orig/arch/ia64/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/ia64/mm/hugetlbpage.c
> @@ -114,6 +114,11 @@ int pud_huge(pud_t pud)
> return 0;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 0;
> +}
> +
> struct page *
> follow_huge_pmd(struct mm_struct *mm, unsigned long address, pmd_t *pmd, int write)
> {
> diff --git v3.11-rc3.orig/arch/metag/mm/hugetlbpage.c v3.11-rc3/arch/metag/mm/hugetlbpage.c
> index 3c52fa6..0424315 100644
> --- v3.11-rc3.orig/arch/metag/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/metag/mm/hugetlbpage.c
> @@ -110,6 +110,11 @@ int pud_huge(pud_t pud)
> return 0;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> +
> struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmd, int write)
> {
> diff --git v3.11-rc3.orig/arch/mips/mm/hugetlbpage.c v3.11-rc3/arch/mips/mm/hugetlbpage.c
> index a7fee0d..01fda44 100644
> --- v3.11-rc3.orig/arch/mips/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/mips/mm/hugetlbpage.c
> @@ -85,6 +85,11 @@ int pud_huge(pud_t pud)
> return (pud_val(pud) & _PAGE_HUGE) != 0;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> +
> struct page *
> follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmd, int write)
> diff --git v3.11-rc3.orig/arch/powerpc/mm/hugetlbpage.c v3.11-rc3/arch/powerpc/mm/hugetlbpage.c
> index 834ca8e..d67db4b 100644
> --- v3.11-rc3.orig/arch/powerpc/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/powerpc/mm/hugetlbpage.c
> @@ -86,6 +86,11 @@ int pgd_huge(pgd_t pgd)
> */
> return ((pgd_val(pgd) & 0x3) != 0x0);
> }
> +
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> #else
> int pmd_huge(pmd_t pmd)
> {
> @@ -101,6 +106,11 @@ int pgd_huge(pgd_t pgd)
> {
> return 0;
> }
> +
> +int pmd_huge_support(void)
> +{
> + return 0;
> +}
> #endif
>
> pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
> diff --git v3.11-rc3.orig/arch/s390/mm/hugetlbpage.c v3.11-rc3/arch/s390/mm/hugetlbpage.c
> index 121089d..951ee25 100644
> --- v3.11-rc3.orig/arch/s390/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/s390/mm/hugetlbpage.c
> @@ -117,6 +117,11 @@ int pud_huge(pud_t pud)
> return 0;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> +
> struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmdp, int write)
> {
> diff --git v3.11-rc3.orig/arch/sh/mm/hugetlbpage.c v3.11-rc3/arch/sh/mm/hugetlbpage.c
> index d776234..0d676a4 100644
> --- v3.11-rc3.orig/arch/sh/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/sh/mm/hugetlbpage.c
> @@ -83,6 +83,11 @@ int pud_huge(pud_t pud)
> return 0;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 0;
> +}
> +
> struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmd, int write)
> {
> diff --git v3.11-rc3.orig/arch/sparc/mm/hugetlbpage.c v3.11-rc3/arch/sparc/mm/hugetlbpage.c
> index d2b5944..9639964 100644
> --- v3.11-rc3.orig/arch/sparc/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/sparc/mm/hugetlbpage.c
> @@ -234,6 +234,11 @@ int pud_huge(pud_t pud)
> return 0;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 0;
> +}
> +
> struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmd, int write)
> {
> diff --git v3.11-rc3.orig/arch/tile/mm/hugetlbpage.c v3.11-rc3/arch/tile/mm/hugetlbpage.c
> index 650ccff..0ac3599 100644
> --- v3.11-rc3.orig/arch/tile/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/tile/mm/hugetlbpage.c
> @@ -198,6 +198,11 @@ int pud_huge(pud_t pud)
> return !!(pud_val(pud) & _PAGE_HUGE_PAGE);
> }
>
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> +
> struct page *follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> pmd_t *pmd, int write)
> {
> diff --git v3.11-rc3.orig/arch/x86/mm/hugetlbpage.c v3.11-rc3/arch/x86/mm/hugetlbpage.c
> index 7e73e8c..9d980d8 100644
> --- v3.11-rc3.orig/arch/x86/mm/hugetlbpage.c
> +++ v3.11-rc3/arch/x86/mm/hugetlbpage.c
> @@ -59,6 +59,10 @@ follow_huge_pmd(struct mm_struct *mm, unsigned long address,
> return NULL;
> }
>
> +int pmd_huge_support(void)
> +{
> + return 0;
> +}
> #else
>
> struct page *
> @@ -77,6 +81,10 @@ int pud_huge(pud_t pud)
> return !!(pud_val(pud) & _PAGE_PSE);
> }
>
> +int pmd_huge_support(void)
> +{
> + return 1;
> +}
> #endif
>
> /* x86_64 also uses this file */
> diff --git v3.11-rc3.orig/include/linux/hugetlb.h v3.11-rc3/include/linux/hugetlb.h
> index 2e02c4e..0393270 100644
> --- v3.11-rc3.orig/include/linux/hugetlb.h
> +++ v3.11-rc3/include/linux/hugetlb.h
> @@ -381,6 +381,16 @@ static inline pgoff_t basepage_index(struct page *page)
>
> extern void dissolve_free_huge_pages(unsigned long start_pfn,
> unsigned long end_pfn);
> +int pmd_huge_support(void);
> +/*
> + * Currently hugepage migration is enabled only for pmd-based hugepage.
> + * This function will be updated when hugepage migration is more widely
> + * supported.
> + */
> +static inline int hugepage_migration_support(struct hstate *h)
> +{
> + return pmd_huge_support() && (huge_page_shift(h) == PMD_SHIFT);
> +}
>
For pmd_huge_support to be true, it needs huge_page_shift == PMD-SHIFT
right ? So why check again ? Also are we only supporting hugepage migration
for hugepages at PMD level ? Why not at other levels ? Also isn't it
better to use zone movable allocation for larger size hugepags ?
-aneesh
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