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
