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Date: Thu, 23 Aug 2012 19:11:56 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Will Deacon <will.deacon@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
linux-arch@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH v2] mm: hugetlb: add arch hook for clearing page flags
before entering pool
On Thu 23-08-12 17:37:13, Will Deacon wrote:
> The core page allocator ensures that page flags are zeroed when freeing
> pages via free_pages_check. A number of architectures (ARM, PPC, MIPS)
> rely on this property to treat new pages as dirty with respect to the
> data cache and perform the appropriate flushing before mapping the pages
> into userspace.
>
> This can lead to cache synchronisation problems when using hugepages,
> since the allocator keeps its own pool of pages above the usual page
> allocator and does not reset the page flags when freeing a page into
> the pool.
>
> This patch adds a new architecture hook, arch_clear_hugepage_flags, so
> that architectures which rely on the page flags being in a particular
> state for fresh allocations can adjust the flags accordingly when a
> page is freed into the pool.
>
> Cc: Michal Hocko <mhocko@...e.cz>
> Signed-off-by: Will Deacon <will.deacon@....com>
Looks good to me
Reviewed-by: Michal Hocko <mhocko@...e.cz>
Thanks!
> ---
>
> v2: Made ia64 and powerpc code a nop, moved hook to free_huge_page
>
> arch/ia64/include/asm/hugetlb.h | 4 ++++
> arch/mips/include/asm/hugetlb.h | 4 ++++
> arch/powerpc/include/asm/hugetlb.h | 4 ++++
> arch/s390/include/asm/hugetlb.h | 1 +
> arch/sh/include/asm/hugetlb.h | 6 ++++++
> arch/sparc/include/asm/hugetlb.h | 4 ++++
> arch/tile/include/asm/hugetlb.h | 4 ++++
> arch/x86/include/asm/hugetlb.h | 4 ++++
> mm/hugetlb.c | 1 +
> 9 files changed, 32 insertions(+), 0 deletions(-)
>
> diff --git a/arch/ia64/include/asm/hugetlb.h b/arch/ia64/include/asm/hugetlb.h
> index da55c63..94eaa5b 100644
> --- a/arch/ia64/include/asm/hugetlb.h
> +++ b/arch/ia64/include/asm/hugetlb.h
> @@ -77,4 +77,8 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> #endif /* _ASM_IA64_HUGETLB_H */
> diff --git a/arch/mips/include/asm/hugetlb.h b/arch/mips/include/asm/hugetlb.h
> index 58d3688..bd94946 100644
> --- a/arch/mips/include/asm/hugetlb.h
> +++ b/arch/mips/include/asm/hugetlb.h
> @@ -112,4 +112,8 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> #endif /* __ASM_HUGETLB_H */
> diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
> index dfdb95b..62e11a3 100644
> --- a/arch/powerpc/include/asm/hugetlb.h
> +++ b/arch/powerpc/include/asm/hugetlb.h
> @@ -151,6 +151,10 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> #else /* ! CONFIG_HUGETLB_PAGE */
> static inline void flush_hugetlb_page(struct vm_area_struct *vma,
> unsigned long vmaddr)
> diff --git a/arch/s390/include/asm/hugetlb.h b/arch/s390/include/asm/hugetlb.h
> index 799ed0f..faa7655 100644
> --- a/arch/s390/include/asm/hugetlb.h
> +++ b/arch/s390/include/asm/hugetlb.h
> @@ -33,6 +33,7 @@ static inline int prepare_hugepage_range(struct file *file,
> }
>
> #define hugetlb_prefault_arch_hook(mm) do { } while (0)
> +#define arch_clear_hugepage_flags(page) do { } while (0)
>
> int arch_prepare_hugepage(struct page *page);
> void arch_release_hugepage(struct page *page);
> diff --git a/arch/sh/include/asm/hugetlb.h b/arch/sh/include/asm/hugetlb.h
> index 967068f..b3808c7 100644
> --- a/arch/sh/include/asm/hugetlb.h
> +++ b/arch/sh/include/asm/hugetlb.h
> @@ -1,6 +1,7 @@
> #ifndef _ASM_SH_HUGETLB_H
> #define _ASM_SH_HUGETLB_H
>
> +#include <asm/cacheflush.h>
> #include <asm/page.h>
>
>
> @@ -89,4 +90,9 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> + clear_bit(PG_dcache_clean, &page->flags);
> +}
> +
> #endif /* _ASM_SH_HUGETLB_H */
> diff --git a/arch/sparc/include/asm/hugetlb.h b/arch/sparc/include/asm/hugetlb.h
> index 1770610..e7927c9 100644
> --- a/arch/sparc/include/asm/hugetlb.h
> +++ b/arch/sparc/include/asm/hugetlb.h
> @@ -82,4 +82,8 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> #endif /* _ASM_SPARC64_HUGETLB_H */
> diff --git a/arch/tile/include/asm/hugetlb.h b/arch/tile/include/asm/hugetlb.h
> index b204238..0f885af 100644
> --- a/arch/tile/include/asm/hugetlb.h
> +++ b/arch/tile/include/asm/hugetlb.h
> @@ -106,6 +106,10 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> #ifdef CONFIG_HUGETLB_SUPER_PAGES
> static inline pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
> struct page *page, int writable)
> diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
> index 439a9ac..bdd35db 100644
> --- a/arch/x86/include/asm/hugetlb.h
> +++ b/arch/x86/include/asm/hugetlb.h
> @@ -90,4 +90,8 @@ static inline void arch_release_hugepage(struct page *page)
> {
> }
>
> +static inline void arch_clear_hugepage_flags(struct page *page)
> +{
> +}
> +
> #endif /* _ASM_X86_HUGETLB_H */
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bc72712..f1bb534 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -637,6 +637,7 @@ static void free_huge_page(struct page *page)
> h->surplus_huge_pages--;
> h->surplus_huge_pages_node[nid]--;
> } else {
> + arch_clear_hugepage_flags(page);
> enqueue_huge_page(h, page);
> }
> spin_unlock(&hugetlb_lock);
> --
> 1.7.4.1
>
--
Michal Hocko
SUSE Labs
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