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    SubjectRe: [PATCH 1/4] pagemap: avoid splitting thp when reading /proc/pid/pagemap
    (12/21/11 5:23 PM), Naoya Horiguchi wrote:
    > Thp split is not necessary if we explicitly check whether pmds are
    > mapping thps or not. This patch introduces the check and the code
    > to generate pagemap entries for pmds mapping thps, which results in
    > less performance impact of pagemap on thp.
    >
    > Signed-off-by: Naoya Horiguchi<n-horiguchi@ah.jp.nec.com>
    > Reviewed-by: Andi Kleen<ak@linux.intel.com>
    >
    > Changes since v1:
    > - move pfn declaration to the beginning of pagemap_pte_range()
    > ---
    > fs/proc/task_mmu.c | 49 +++++++++++++++++++++++++++++++++++++++++++------
    > 1 files changed, 43 insertions(+), 6 deletions(-)
    >
    > diff --git 3.2-rc5.orig/fs/proc/task_mmu.c 3.2-rc5/fs/proc/task_mmu.c
    > index e418c5a..0df61ab 100644
    > --- 3.2-rc5.orig/fs/proc/task_mmu.c
    > +++ 3.2-rc5/fs/proc/task_mmu.c
    > @@ -600,6 +600,9 @@ struct pagemapread {
    > u64 *buffer;
    > };
    >
    > +#define PAGEMAP_WALK_SIZE (PMD_SIZE)
    > +#define PAGEMAP_WALK_MASK (PMD_MASK)
    > +
    > #define PM_ENTRY_BYTES sizeof(u64)
    > #define PM_STATUS_BITS 3
    > #define PM_STATUS_OFFSET (64 - PM_STATUS_BITS)
    > @@ -658,6 +661,22 @@ static u64 pte_to_pagemap_entry(pte_t pte)
    > return pme;
    > }
    >
    > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
    > +static u64 thp_pte_to_pagemap_entry(pte_t pte, int offset)
    > +{
    > + u64 pme = 0;
    > + if (pte_present(pte))

    When does pte_present() return 0?

    > + pme = PM_PFRAME(pte_pfn(pte) + offset)
    > + | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT;
    > + return pme;
    > +}
    > +#else
    > +static inline u64 thp_pte_to_pagemap_entry(pte_t pte, int offset)
    > +{
    > + return 0;
    > +}
    > +#endif
    > +
    > static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
    > struct mm_walk *walk)
    > {
    > @@ -665,14 +684,34 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
    > struct pagemapread *pm = walk->private;
    > pte_t *pte;
    > int err = 0;
    > -
    > - split_huge_page_pmd(walk->mm, pmd);
    > + u64 pfn = PM_NOT_PRESENT;
    >
    > /* find the first VMA at or above 'addr' */
    > vma = find_vma(walk->mm, addr);
    > - for (; addr != end; addr += PAGE_SIZE) {
    > - u64 pfn = PM_NOT_PRESENT;
    >
    > + spin_lock(&walk->mm->page_table_lock);
    > + if (pmd_trans_huge(*pmd)) {
    > + if (pmd_trans_splitting(*pmd)) {
    > + spin_unlock(&walk->mm->page_table_lock);
    > + wait_split_huge_page(vma->anon_vma, pmd);
    > + } else {
    > + for (; addr != end; addr += PAGE_SIZE) {
    > + int offset = (addr& ~PAGEMAP_WALK_MASK)
    > + >> PAGE_SHIFT;

    implicit narrowing conversion. offset should be unsigned long.


    > + pfn = thp_pte_to_pagemap_entry(*(pte_t *)pmd,
    > + offset);

    This (pte_t*) cast looks introduce new implicit assumption. Please don't
    put x86 assumption here directly.




    > + err = add_to_pagemap(addr, pfn, pm);
    > + if (err)
    > + break;
    > + }
    > + spin_unlock(&walk->mm->page_table_lock);
    > + return err;
    > + }
    > + } else {
    > + spin_unlock(&walk->mm->page_table_lock);
    > + }

    coding standard violation. plz run check_patch.pl.




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