Re: [PATCH 2/2] mm: khugepaged: check MMF_DISABLE_THP ahead of iterating over vmas

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 





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@xxxxxxxxxxxxx> wrote:

From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
---
  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






[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux