| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAK1f24=2z9tk4cCCSobVpExZ+uV6N8gbGx+xiJ7p_UjrZvSv3g@mail.gmail.com>
Date: Sat, 24 Feb 2024 11:54:20 +0800
From: Lance Yang <ioworker0@...il.com>
To: Yang Shi <shy828301@...il.com>
Cc: akpm@...ux-foundation.org, mhocko@...e.com, zokeefe@...gle.com,
david@...hat.com, songmuchun@...edance.com, peterx@...hat.com,
minchan@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/khugepaged: bypassing unnecessary scans with
MMF_DISABLE_THP check
Hey Yang,
Thanks for taking time to review!
On Sat, Feb 24, 2024 at 9:46 AM Yang Shi <shy828301@...il.com> wrote:
>
> On Sun, Jan 28, 2024 at 9:46 PM Lance Yang <ioworker0@...il.com> wrote:
> >
> > khugepaged scans the entire address space in the
> > background for each given mm, looking for
> > opportunities to merge sequences of basic pages
> > into huge pages. However, when an mm is inserted
> > to the mm_slots list, and the MMF_DISABLE_THP flag
> > is set later, this scanning process becomes
> > unnecessary for that mm and can be skipped to avoid
> > redundant operations, especially in scenarios with
> > a large address space.
> >
> > This commit introduces a check before each scanning
> > process to test the MMF_DISABLE_THP flag for the
> > given mm; if the flag is set, the scanning process
> > is bypassed, thereby improving the efficiency of
> > khugepaged.
> >
> > Signed-off-by: Lance Yang <ioworker0@...il.com>
> > ---
> > mm/khugepaged.c | 18 ++++++++++++------
> > 1 file changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 2b219acb528e..d6a700834edc 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -410,6 +410,12 @@ static inline int hpage_collapse_test_exit(struct mm_struct *mm)
> > return atomic_read(&mm->mm_users) == 0;
> > }
> >
> > +static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *mm)
> > +{
> > + return hpage_collapse_test_exit(mm) ||
> > + test_bit(MMF_DISABLE_THP, &mm->flags);
> > +}
> > +
> > void __khugepaged_enter(struct mm_struct *mm)
> > {
> > struct khugepaged_mm_slot *mm_slot;
> > @@ -1422,7 +1428,7 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
> >
> > lockdep_assert_held(&khugepaged_mm_lock);
> >
> > - if (hpage_collapse_test_exit(mm)) {
> > + if (hpage_collapse_test_exit_or_disable(mm)) {
>
> I'm not quite sure whether we should remove the mm from mm_slot and
> drop mm_count or not since clearing MMF_THP_DISABLE flag doesn't add
> the mm back. Creating new vma may add the mm back, but I don't think
> the behavior should depend on this.
Thanks for bringing this up! I agree with your point.
I'll remove the MMF_THP_DISABLE flag check in
collect_mm_slot().
>
> > /* free mm_slot */
> > hash_del(&slot->hash);
> > list_del(&slot->mm_node);
> > @@ -2360,7 +2366,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> > goto breakouterloop_mmap_lock;
> >
> > progress++;
> > - if (unlikely(hpage_collapse_test_exit(mm)))
> > + if (unlikely(hpage_collapse_test_exit_or_disable(mm)))
> > goto breakouterloop;
> >
> > vma_iter_init(&vmi, mm, khugepaged_scan.address);
> > @@ -2368,7 +2374,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> > unsigned long hstart, hend;
> >
> > cond_resched();
> > - if (unlikely(hpage_collapse_test_exit(mm))) {
> > + if (unlikely(hpage_collapse_test_exit_or_disable(mm))) {
> > progress++;
> > break;
> > }
> > @@ -2390,7 +2396,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> > bool mmap_locked = true;
> >
> > cond_resched();
> > - if (unlikely(hpage_collapse_test_exit(mm)))
> > + if (unlikely(hpage_collapse_test_exit_or_disable(mm)))
> > goto breakouterloop;
> >
> > VM_BUG_ON(khugepaged_scan.address < hstart ||
> > @@ -2408,7 +2414,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> > fput(file);
> > if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
> > mmap_read_lock(mm);
> > - if (hpage_collapse_test_exit(mm))
> > + if (hpage_collapse_test_exit_or_disable(mm))
> > goto breakouterloop;
> > *result = collapse_pte_mapped_thp(mm,
> > khugepaged_scan.address, false);
> > @@ -2450,7 +2456,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
> > * Release the current mm_slot if this mm is about to die, or
> > * if we scanned all vmas of this mm.
> > */
> > - if (hpage_collapse_test_exit(mm) || !vma) {
> > + if (hpage_collapse_test_exit_or_disable(mm) || !vma) {
>
> Same like the above comment.
I‘ll also remove the MMF_THP_DISABLE flag check here.
>
> In addition, didn't you need to change hpage_collapse_test_exit() to
> hpage_collapse_test_exit_or_disable() in hugepage_vma_revalidate()?
Thanks for your suggestion! It makes sense to change
hpage_collapse_test_exit() to hpage_collapse_test_exit_or_disable()
in hugepage_vma_revalidate().
Thanks again for your time!
Lance
>
> > /*
> > * Make sure that if mm_users is reaching zero while
> > * khugepaged runs here, khugepaged_exit will find
> > --
> > 2.33.1
> >
Powered by blists - more mailing lists