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dkim=pass header.d=gmail.com header.s=20210112 header.b=oSwJGIdX; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf16.hostedemail.com: domain of shy828301@gmail.com designates 209.85.214.180 as permitted sender) smtp.mailfrom=shy828301@gmail.com X-Rspamd-Server: rspam10 X-HE-Tag: 1655315384-829439 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Jun 11, 2022 at 1:47 AM Miaohe Lin wrote: > > When do_swap_page returns VM_FAULT_RETRY, we do not retry here and thus > swap entry will remain in pagetable. This will result in later failure. > So stop swapping in pages in this case to save cpu cycles. > > Signed-off-by: Miaohe Lin > --- > mm/khugepaged.c | 19 ++++++++----------- > 1 file changed, 8 insertions(+), 11 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 73570dfffcec..a8adb2d1e9c6 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1003,19 +1003,16 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm, > swapped_in++; > ret = do_swap_page(&vmf); > > - /* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */ > + /* > + * do_swap_page returns VM_FAULT_RETRY with released mmap_lock. > + * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because > + * we do not retry here and swap entry will remain in pagetable > + * resulting in later failure. Yeah, it makes sense. > + */ > if (ret & VM_FAULT_RETRY) { > mmap_read_lock(mm); A further optimization, you should not need to relock mmap_lock. You may consider returning a different value or passing in *locked and setting it to false, then check this value in the caller to skip unlock. > - if (hugepage_vma_revalidate(mm, haddr, &vma)) { > - /* vma is no longer available, don't continue to swapin */ > - trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); > - return false; > - } > - /* check if the pmd is still valid */ > - if (mm_find_pmd(mm, haddr) != pmd) { > - trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); > - return false; > - } > + trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); > + return false; > } > if (ret & VM_FAULT_ERROR) { > trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); And I think "swapped_in++" needs to be moved after error handling. > -- > 2.23.0 > >