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    Subject[PATCH 17/21] mm: batch updating mm_counters
    tlb_finish_mmu used to batch zap_pte_range's update of mm rss, which may
    be worthwhile if the mm is contended, and would reduce atomic operations
    if the counts were atomic. Let zap_pte_range now batch its updates to
    file_rss and anon_rss, per page-table in case we drop the lock outside;
    and copy_pte_range batch them too.

    Signed-off-by: Hugh Dickins <hugh@veritas.com>
    ---

    mm/memory.c | 47 ++++++++++++++++++++++++++++++++---------------
    1 files changed, 32 insertions(+), 15 deletions(-)

    --- mm16/mm/memory.c 2005-09-24 19:29:53.000000000 +0100
    +++ mm17/mm/memory.c 2005-09-24 19:30:07.000000000 +0100
    @@ -332,6 +332,16 @@ out:
    return pte_offset_kernel(pmd, address);
    }

    +static inline void add_mm_rss(struct mm_struct *mm, int file_rss, int anon_rss)
    +{
    + if (file_rss)
    + add_mm_counter(mm, file_rss, file_rss);
    + if (anon_rss)
    + add_mm_counter(mm, anon_rss, anon_rss);
    +}
    +
    +#define NO_RSS 2 /* Increment neither file_rss nor anon_rss */
    +
    /*
    * copy one vm_area from one task to the other. Assumes the page tables
    * already present in the new task to be cleared in the whole range
    @@ -341,7 +351,7 @@ out:
    * but may be dropped within p[mg]d_alloc() and pte_alloc_map().
    */

    -static inline void
    +static inline int
    copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
    pte_t *dst_pte, pte_t *src_pte, unsigned long vm_flags,
    unsigned long addr)
    @@ -349,6 +359,7 @@ copy_one_pte(struct mm_struct *dst_mm, s
    pte_t pte = *src_pte;
    struct page *page;
    unsigned long pfn;
    + int anon = NO_RSS;

    /* pte contains position in swap or file, so copy. */
    if (unlikely(!pte_present(pte))) {
    @@ -361,8 +372,7 @@ copy_one_pte(struct mm_struct *dst_mm, s
    spin_unlock(&mmlist_lock);
    }
    }
    - set_pte_at(dst_mm, addr, dst_pte, pte);
    - return;
    + goto out_set_pte;
    }

    pfn = pte_pfn(pte);
    @@ -375,10 +385,8 @@ copy_one_pte(struct mm_struct *dst_mm, s
    if (pfn_valid(pfn))
    page = pfn_to_page(pfn);

    - if (!page || PageReserved(page)) {
    - set_pte_at(dst_mm, addr, dst_pte, pte);
    - return;
    - }
    + if (!page || PageReserved(page))
    + goto out_set_pte;

    /*
    * If it's a COW mapping, write protect it both
    @@ -397,12 +405,12 @@ copy_one_pte(struct mm_struct *dst_mm, s
    pte = pte_mkclean(pte);
    pte = pte_mkold(pte);
    get_page(page);
    - if (PageAnon(page))
    - inc_mm_counter(dst_mm, anon_rss);
    - else
    - inc_mm_counter(dst_mm, file_rss);
    - set_pte_at(dst_mm, addr, dst_pte, pte);
    page_dup_rmap(page);
    + anon = !!PageAnon(page);
    +
    +out_set_pte:
    + set_pte_at(dst_mm, addr, dst_pte, pte);
    + return anon;
    }

    static int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
    @@ -412,8 +420,10 @@ static int copy_pte_range(struct mm_stru
    pte_t *src_pte, *dst_pte;
    unsigned long vm_flags = vma->vm_flags;
    int progress = 0;
    + int rss[NO_RSS+1], anon;

    again:
    + rss[1] = rss[0] = 0;
    dst_pte = pte_alloc_map(dst_mm, dst_pmd, addr);
    if (!dst_pte)
    return -ENOMEM;
    @@ -436,13 +446,16 @@ again:
    progress++;
    continue;
    }
    - copy_one_pte(dst_mm, src_mm, dst_pte, src_pte, vm_flags, addr);
    + anon = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte,
    + vm_flags, addr);
    + rss[anon]++;
    progress += 8;
    } while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);
    spin_unlock(&src_mm->page_table_lock);

    pte_unmap_nested(src_pte - 1);
    pte_unmap(dst_pte - 1);
    + add_mm_rss(dst_mm, rss[0], rss[1]);
    cond_resched_lock(&dst_mm->page_table_lock);
    if (addr != end)
    goto again;
    @@ -533,6 +546,8 @@ static void zap_pte_range(struct mmu_gat
    struct zap_details *details)
    {
    pte_t *pte;
    + int file_rss = 0;
    + int anon_rss = 0;

    pte = pte_offset_map(pmd, addr);
    do {
    @@ -576,13 +591,13 @@ static void zap_pte_range(struct mmu_gat
    set_pte_at(tlb->mm, addr, pte,
    pgoff_to_pte(page->index));
    if (PageAnon(page))
    - dec_mm_counter(tlb->mm, anon_rss);
    + anon_rss++;
    else {
    if (pte_dirty(ptent))
    set_page_dirty(page);
    if (pte_young(ptent))
    mark_page_accessed(page);
    - dec_mm_counter(tlb->mm, file_rss);
    + file_rss++;
    }
    page_remove_rmap(page);
    tlb_remove_page(tlb, page);
    @@ -598,6 +613,8 @@ static void zap_pte_range(struct mmu_gat
    free_swap_and_cache(pte_to_swp_entry(ptent));
    pte_clear_full(tlb->mm, addr, pte, tlb->fullmm);
    } while (pte++, addr += PAGE_SIZE, addr != end);
    +
    + add_mm_rss(tlb->mm, -file_rss, -anon_rss);
    pte_unmap(pte - 1);
    }

    -
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