Messages in this thread | | | Subject | Re: [PATCHv3, RESEND 2/8] khugepaged: Do not stop collapse if less than half PTEs are referenced | From | Yang Shi <> | Date | Wed, 15 Apr 2020 13:31:33 -0700 |
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On 4/13/20 5:52 AM, Kirill A. Shutemov wrote: > __collapse_huge_page_swapin() checks the number of referenced PTE to > decide if the memory range is hot enough to justify swapin. > > We have few problems with the approach: > > - It is way too late: we can do the check much earlier and safe time. > khugepaged_scan_pmd() already knows if we have any pages to swap in > and number of referenced page. > > - It stops collapse altogether if there's not enough referenced pages, > not only swappingin. > > Fix it by making the right check early. We also can avoid additional > page table scanning if khugepaged_scan_pmd() haven't found any swap > entries. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative") > --- > mm/khugepaged.c | 25 ++++++++++--------------- > 1 file changed, 10 insertions(+), 15 deletions(-)
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Just a nit below.
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 99bab7e4d05b..5968ec5ddd6b 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -902,11 +902,6 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > .pgoff = linear_page_index(vma, address), > }; > > - /* we only decide to swapin, if there is enough young ptes */ > - if (referenced < HPAGE_PMD_NR/2) { > - trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); > - return false; > - } > vmf.pte = pte_offset_map(pmd, address); > for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE; > vmf.pte++, vmf.address += PAGE_SIZE) { > @@ -946,7 +941,7 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > static void collapse_huge_page(struct mm_struct *mm, > unsigned long address, > struct page **hpage, > - int node, int referenced) > + int node, int referenced, int unmapped) > { > pmd_t *pmd, _pmd; > pte_t *pte; > @@ -1003,7 +998,8 @@ static void collapse_huge_page(struct mm_struct *mm, > * If it fails, we release mmap_sem and jump out_nolock. > * Continuing to collapse causes inconsistency. > */ > - if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) { > + if (unmapped && !__collapse_huge_page_swapin(mm, vma, address, > + pmd, referenced)) { > mem_cgroup_cancel_charge(new_page, memcg, true); > up_read(&mm->mmap_sem); > goto out_nolock; > @@ -1214,22 +1210,21 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > mmu_notifier_test_young(vma->vm_mm, address)) > referenced++; > } > - if (writable) { > - if (referenced) { > + if (!writable) { > + result = SCAN_PAGE_RO; > + } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) { > + result = SCAN_LACK_REFERENCED_PAGE; > + } else { > result = SCAN_SUCCEED; > ret = 1;
Shall fix the indentation for the above two statements?
> - } else { > - result = SCAN_LACK_REFERENCED_PAGE; > - } > - } else { > - result = SCAN_PAGE_RO; > } > out_unmap: > pte_unmap_unlock(pte, ptl); > if (ret) { > node = khugepaged_find_target_node(); > /* collapse_huge_page will return with the mmap_sem released */ > - collapse_huge_page(mm, address, hpage, node, referenced); > + collapse_huge_page(mm, address, hpage, node, > + referenced, unmapped); > } > out: > trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
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