On Tue, Oct 28, 2014 at 03:18:10PM +0200, Kirill A. Shutemov wrote:
> On Tue, Oct 28, 2014 at 11:18:38PM +0800, Fengwei Yin wrote:
> > On Mon, Oct 27, 2014 at 03:17:48PM -0700, Andrew Morton wrote:
> > > On Mon, 27 Oct 2014 23:02:13 +0800 Fengwei Yin <yfw.kernel@xxxxxxxxx> wrote:
> > >
> > > > We could see following memory info in /proc/xxxx/smaps with THP enabled.
> > > > 7bea458b3000-7fea458b3000 r--p 00000000 00:13 39989 /dev/zero
> > > > Size: 4294967296 kB
> > > > Rss: 10612736 kB
> > > > Pss: 10612736 kB
> > > > Shared_Clean: 0 kB
> > > > Shared_Dirty: 0 kB
> > > > Private_Clean: 10612736 kB
> > > > Private_Dirty: 0 kB
> > > > Referenced: 10612736 kB
> > > > Anonymous: 0 kB
> > > > AnonHugePages: 10612736 kB
> > > > Swap: 0 kB
> > > > KernelPageSize: 4 kB
> > > > MMUPageSize: 4 kB
> > > > Locked: 0 kB
> > > > VmFlags: rd mr mw me
> > > > which is wrong becuase just huge_zero_page/normal_zero_page is used for
> > > > /dev/zero. Most of the value should be 0.
> > > >
> > > > This patch detects huge_zero_page (original implementation just detect
> > > > normal_zero_page) and avoids to update the wrong value for huge_zero_page.
> > > >
> > > > ...
> > > >
> > > > --- a/mm/memory.c
> > > > +++ b/mm/memory.c
> > > > @@ -41,6 +41,7 @@
> > > > #include <linux/kernel_stat.h>
> > > > #include <linux/mm.h>
> > > > #include <linux/hugetlb.h>
> > > > +#include <linux/huge_mm.h>
> > > > #include <linux/mman.h>
> > > > #include <linux/swap.h>
> > > > #include <linux/highmem.h>
> > > > @@ -787,6 +788,9 @@ check_pfn:
> > > > return NULL;
> > > > }
> > > >
> > > > + if (is_huge_zero_pfn(pfn))
> > > > + return NULL;
> > > > +
> > >
> > > Why this change?
> > >
> > I suppose the huge zero page should have same behavior as normal zero
> > page. vm_normal_page will return NULL if the pte is for normal zero
> > page. This change make it return NULL for huge zero page.
> >
> > > What effect does it have upon vm_normal_page()'s many existing callers?
> > This is good question. I suppose it will not impact existing caller.
>
> vm_normal_page() is designed to handle pte. We only get there due hack
> with pmd to pte cast in smaps_pte_range(). Let's try to get rid of it
> instead.
>
> Could you test the patch below? I think it's a better fix.
I will test the patch tomorrow and let you know the result. Thanks.
>
> From 592a7e789128d92e7f5165b583558443e82c88fd Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Tue, 28 Oct 2014 14:51:31 +0200
> Subject: [PATCH] mm: fix huge zero page accounting in smaps report
>
> As a small zero page, huge zero page should not be accounted in smaps
> report as normal page.
>
> For small pages we rely on vm_normal_page() to filter out zero page, but
> vm_normal_page() is not designed to handle pmds. We only get here due
> hackish cast pmd to pte in smaps_pte_range() -- pte and pmd format is
> not necessary compatible on each and every architecture.
>
> Let's add separate codepath to handle pmds. follow_trans_huge_pmd() will
> detect huge zero page for us.
>
> We would need pmd_dirty() helper to do this properly. The patch adds it
> to THP-enabled architectures which don't yet have one.
>
> Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> arch/arm64/include/asm/pgtable.h | 1 +
> arch/powerpc/include/asm/pgtable-ppc64.h | 1 +
> arch/sparc/include/asm/pgtable_64.h | 7 +++
> arch/x86/include/asm/pgtable.h | 5 ++
> fs/proc/task_mmu.c | 101 ++++++++++++++++++++-----------
> 5 files changed, 79 insertions(+), 36 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 41a43bf26492..df22314f57cf 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -279,6 +279,7 @@ void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
> #endif /* CONFIG_HAVE_RCU_TABLE_FREE */
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>
> +#define pmd_dirty(pmd) pte_dirty(pmd_pte(pmd))
> #define pmd_young(pmd) pte_young(pmd_pte(pmd))
> #define pmd_wrprotect(pmd) pte_pmd(pte_wrprotect(pmd_pte(pmd)))
> #define pmd_mksplitting(pmd) pte_pmd(pte_mkspecial(pmd_pte(pmd)))
> diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
> index ae153c40ab7c..9b4b1904efae 100644
> --- a/arch/powerpc/include/asm/pgtable-ppc64.h
> +++ b/arch/powerpc/include/asm/pgtable-ppc64.h
> @@ -467,6 +467,7 @@ static inline pte_t *pmdp_ptep(pmd_t *pmd)
> }
>
> #define pmd_pfn(pmd) pte_pfn(pmd_pte(pmd))
> +#define pmd_dirty(pmd) pte_dirty(pmd_pte(pmd))
> #define pmd_young(pmd) pte_young(pmd_pte(pmd))
> #define pmd_mkold(pmd) pte_pmd(pte_mkold(pmd_pte(pmd)))
> #define pmd_wrprotect(pmd) pte_pmd(pte_wrprotect(pmd_pte(pmd)))
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index bfeb626085ac..90af17ee6184 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -667,6 +667,13 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
> }
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static inline pmd_t pmd_dirty(pmd_t pmd)
> +{
> + pte_t pte = __pte(pmd_val(pmd));
> +
> + return pte_dirty(pte);
> +}
> +
> static inline unsigned long pmd_young(pmd_t pmd)
> {
> pte_t pte = __pte(pmd_val(pmd));
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index aa97a070f09f..081d6f45e006 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -99,6 +99,11 @@ static inline int pte_young(pte_t pte)
> return pte_flags(pte) & _PAGE_ACCESSED;
> }
>
> +static inline int pmd_dirty(pmd_t pmd)
> +{
> + return pmd_flags(pmd) & _PAGE_DIRTY;
> +}
> +
> static inline int pmd_young(pmd_t pmd)
> {
> return pmd_flags(pmd) & _PAGE_ACCESSED;
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 4e0388cffe3d..2ab200d429be 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -447,58 +447,88 @@ struct mem_size_stats {
> u64 pss;
> };
>
> +static void smaps_account(struct mem_size_stats *mss, struct page *page,
> + unsigned long size, bool young, bool dirty)
> +{
> + int mapcount;
> +
> + if (PageAnon(page))
> + mss->anonymous += size;
>
> -static void smaps_pte_entry(pte_t ptent, unsigned long addr,
> - unsigned long ptent_size, struct mm_walk *walk)
> + mss->resident += size;
> + /* Accumulate the size in pages that have been accessed. */
> + if (young || PageReferenced(page))
> + mss->referenced += size;
> + mapcount = page_mapcount(page);
> + if (mapcount >= 2) {
> + if (dirty || PageDirty(page))
> + mss->shared_dirty += size;
> + else
> + mss->shared_clean += size;
> + mss->pss += (size << PSS_SHIFT) / mapcount;
> + } else {
> + if (dirty || PageDirty(page))
> + mss->private_dirty += size;
> + else
> + mss->private_clean += size;
> + mss->pss += (size << PSS_SHIFT);
> + }
> +}
> +
> +
> +static void smaps_pte_entry(pte_t *pte, unsigned long addr,
> + struct mm_walk *walk)
> {
> struct mem_size_stats *mss = walk->private;
> struct vm_area_struct *vma = mss->vma;
> pgoff_t pgoff = linear_page_index(vma, addr);
> struct page *page = NULL;
> - int mapcount;
>
> - if (pte_present(ptent)) {
> - page = vm_normal_page(vma, addr, ptent);
> - } else if (is_swap_pte(ptent)) {
> - swp_entry_t swpent = pte_to_swp_entry(ptent);
> + if (pte_present(*pte)) {
> + page = vm_normal_page(vma, addr, *pte);
> + } else if (is_swap_pte(*pte)) {
> + swp_entry_t swpent = pte_to_swp_entry(*pte);
>
> if (!non_swap_entry(swpent))
> - mss->swap += ptent_size;
> + mss->swap += PAGE_SIZE;
> else if (is_migration_entry(swpent))
> page = migration_entry_to_page(swpent);
> - } else if (pte_file(ptent)) {
> - if (pte_to_pgoff(ptent) != pgoff)
> - mss->nonlinear += ptent_size;
> + } else if (pte_file(*pte)) {
> + if (pte_to_pgoff(*pte) != pgoff)
> + mss->nonlinear += PAGE_SIZE;
> }
>
> if (!page)
> return;
>
> - if (PageAnon(page))
> - mss->anonymous += ptent_size;
> -
> if (page->index != pgoff)
> - mss->nonlinear += ptent_size;
> + mss->nonlinear += PAGE_SIZE;
>
> - mss->resident += ptent_size;
> - /* Accumulate the size in pages that have been accessed. */
> - if (pte_young(ptent) || PageReferenced(page))
> - mss->referenced += ptent_size;
> - mapcount = page_mapcount(page);
> - if (mapcount >= 2) {
> - if (pte_dirty(ptent) || PageDirty(page))
> - mss->shared_dirty += ptent_size;
> - else
> - mss->shared_clean += ptent_size;
> - mss->pss += (ptent_size << PSS_SHIFT) / mapcount;
> - } else {
> - if (pte_dirty(ptent) || PageDirty(page))
> - mss->private_dirty += ptent_size;
> - else
> - mss->private_clean += ptent_size;
> - mss->pss += (ptent_size << PSS_SHIFT);
> - }
> + smaps_account(mss, page, PAGE_SIZE, pte_young(*pte), pte_dirty(*pte));
> +}
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
> + struct mm_walk *walk)
> +{
> + struct mem_size_stats *mss = walk->private;
> + struct vm_area_struct *vma = mss->vma;
> + struct page *page;
> +
> + /* FOLL_DUMP will return -EFAULT on huge zero page */
> + page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
> + if (IS_ERR_OR_NULL(page))
> + return;
> + mss->anonymous_thp += HPAGE_PMD_SIZE;
> + smaps_account(mss, page, HPAGE_PMD_SIZE,
> + pmd_young(*pmd), pmd_dirty(*pmd));
> }
> +#else
> +static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
> + struct mm_walk *walk)
> +{
> +}
> +#endif
>
> static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> struct mm_walk *walk)
> @@ -509,9 +539,8 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> spinlock_t *ptl;
>
> if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
> - smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_PMD_SIZE, walk);
> + smaps_pmd_entry(pmd, addr, walk);
> spin_unlock(ptl);
> - mss->anonymous_thp += HPAGE_PMD_SIZE;
> return 0;
> }
>
> @@ -524,7 +553,7 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> */
> pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> for (; addr != end; pte++, addr += PAGE_SIZE)
> - smaps_pte_entry(*pte, addr, PAGE_SIZE, walk);
> + smaps_pte_entry(pte, addr, walk);
> pte_unmap_unlock(pte - 1, ptl);
> cond_resched();
> return 0;
> --
> Kirill A. Shutemov
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