Messages in this thread | | | Subject | Re: [PATCH 2/2] mm: khugepaged: check MMF_DISABLE_THP ahead of iterating over vmas | From | "Xu, Yanfei" <> | Date | Tue, 6 Apr 2021 10:51:46 +0800 |
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On 4/6/21 2:20 AM, Yang Shi wrote: > [Please note: This e-mail is from an EXTERNAL e-mail address] > > On Sun, Apr 4, 2021 at 8:33 AM <yanfei.xu@windriver.com> wrote: >> >> From: Yanfei Xu <yanfei.xu@windriver.com> >> >> We could check MMF_DISABLE_THP ahead of iterating over all of vma. >> Otherwise if some mm_struct contain a large number of vma, there will >> be amounts meaningless cpu cycles cost. >> >> BTW, drop an unnecessary cond_resched(), because there is a another >> cond_resched() followed it and no consumed invocation between them. >> >> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com> >> --- >> mm/khugepaged.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >> index 2efe1d0c92ed..c293ec4a94ea 100644 >> --- a/mm/khugepaged.c >> +++ b/mm/khugepaged.c >> @@ -2094,6 +2094,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, >> */ >> if (unlikely(!mmap_read_trylock(mm))) >> goto breakouterloop_mmap_lock; >> + if (test_bit(MMF_DISABLE_THP, &mm->flags)) >> + goto breakouterloop_mmap_lock; > > It is fine to check this flag. But mmap_lock has been acquired so you > should jump to breakouterloop.
Oops! It's my fault. Thank you for pointing out this. Will fix it in v2.
> >> if (likely(!khugepaged_test_exit(mm))) >> vma = find_vma(mm, khugepaged_scan.address); >> >> @@ -2101,7 +2103,6 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, >> for (; vma; vma = vma->vm_next) { >> unsigned long hstart, hend; >> >> - cond_resched(); > > I don't have a strong opinion for removing this cond_resched(). But > IIUC khugepaged is a best effort job there is no harm to keep it IMHO. >
Yes, keeping it is no harm. But I think we should add it when we need. Look at the blow codes, there are only some simple check between these two cond_resched(). And we still have some cond_resched() in the khugepaged_scan_file() and khugepaged_scan_pmd() which is the actual wrok about collapsing. So I think it is unnecessary. :)
for (; vma; vma = vma->vm_next) { unsigned long hstart, hend;
cond_resched(); //here if (unlikely(khugepaged_test_exit(mm))) { progress++; break; } if (!hugepage_vma_check(vma, vma->vm_flags)) { skip: progress++; continue; } hstart = ALIGN(vma->vm_start, HPAGE_PMD_SIZE); hend = ALIGN_DOWN(vma->vm_end, HPAGE_PMD_SIZE); if (hstart >= hend) goto skip; if (khugepaged_scan.address > hend) goto skip; if (khugepaged_scan.address < hstart) khugepaged_scan.address = hstart; VM_BUG_ON(!IS_ALIGNED(khugepaged_scan.address, HPAGE_PMD_SIZE));
if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma)) goto skip;
while (khugepaged_scan.address < hend) { int ret; cond_resched(); //here
>> if (unlikely(khugepaged_test_exit(mm))) { >> progress++; >> break; >> -- >> 2.27.0 >> >>
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