Re: [PATCH RFC 1/4] mm: throttle MADV_FREE

From: Michal Hocko
Date: Wed Feb 25 2015 - 10:07:44 EST


On Wed 25-02-15 16:11:18, Minchan Kim wrote:
[...]
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 6d0fcb8921c2..d41ae76d3e54 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -274,7 +274,9 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> spinlock_t *ptl;
> pte_t *pte, ptent;
> struct page *page;
> + swp_entry_t entry;
> unsigned long next;
> + int rss = 0;
>
> next = pmd_addr_end(addr, end);
> if (pmd_trans_huge(*pmd)) {
> @@ -293,9 +295,19 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> for (; addr != end; pte++, addr += PAGE_SIZE) {
> ptent = *pte;
>
> - if (!pte_present(ptent))
> + if (pte_none(ptent))
> continue;
>
> + if (!pte_present(ptent)) {
> + entry = pte_to_swp_entry(ptent);
> + if (non_swap_entry(entry))
> + continue;
> + rss--;
> + free_swap_and_cache(entry);
> + pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
> + continue;
> + }

Yes this makes sense. rss is a bit confusing because those pages are not
resident.

> +
> page = vm_normal_page(vma, addr, ptent);
> if (!page)
> continue;
> @@ -326,6 +338,14 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
> set_pte_at(mm, addr, pte, ptent);
> tlb_remove_tlb_entry(tlb, pte, addr);
> }
> +
> + if (rss) {
> + if (current->mm == mm)
> + sync_mm_rss(mm);
> +
> + add_mm_counter(mm, MM_SWAPENTS, rss);
> + }
> +
> arch_leave_lazy_mmu_mode();
> pte_unmap_unlock(pte - 1, ptl);
> next:
> --
> 1.9.1
--
Michal Hocko
SUSE Labs
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