From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Yang Shi <shy828301@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Linux MM <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 5/7] khugepaged: Allow to collapse PTE-mapped compound pages
Date: Sat, 28 Mar 2020 03:34:24 +0300 [thread overview]
Message-ID: <20200328003424.kusu2xnhnlbmnfzl@box> (raw)
In-Reply-To: <CAHbLzkoVq-ssduiPwdzcsL2bVhPwmw4X9ktAO0CYOVAi8H84oA@mail.gmail.com>
On Fri, Mar 27, 2020 at 11:53:57AM -0700, Yang Shi wrote:
> On Fri, Mar 27, 2020 at 10:06 AM Kirill A. Shutemov
> <kirill@shutemov.name> wrote:
> >
> > We can collapse PTE-mapped compound pages. We only need to avoid
> > handling them more than once: lock/unlock page only once if it's present
> > in the PMD range multiple times as it handled on compound level. The
> > same goes for LRU isolation and putpack.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> > mm/khugepaged.c | 41 +++++++++++++++++++++++++++++++----------
> > 1 file changed, 31 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index b47edfe57f7b..c8c2c463095c 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -515,6 +515,17 @@ void __khugepaged_exit(struct mm_struct *mm)
> >
> > static void release_pte_page(struct page *page)
> > {
> > + /*
> > + * We need to unlock and put compound page on LRU only once.
> > + * The rest of the pages have to be locked and not on LRU here.
> > + */
> > + VM_BUG_ON_PAGE(!PageCompound(page) &&
> > + (!PageLocked(page) && PageLRU(page)), page);
> > +
> > + if (!PageLocked(page))
> > + return;
> > +
> > + page = compound_head(page);
> > dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
>
> We need count in the number of base pages. The same counter is
> modified by vmscan in base page unit.
Is it though? Where?
> Also need modify the inc path.
Done already.
> > unlock_page(page);
> > putback_lru_page(page);
> > @@ -537,6 +548,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> > pte_t *_pte;
> > int none_or_zero = 0, result = 0, referenced = 0;
> > bool writable = false;
> > + LIST_HEAD(compound_pagelist);
> >
> > for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
> > _pte++, address += PAGE_SIZE) {
> > @@ -561,13 +573,23 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> > goto out;
> > }
> >
> > - /* TODO: teach khugepaged to collapse THP mapped with pte */
> > + VM_BUG_ON_PAGE(!PageAnon(page), page);
> > +
> > if (PageCompound(page)) {
> > - result = SCAN_PAGE_COMPOUND;
> > - goto out;
> > - }
> > + struct page *p;
> > + page = compound_head(page);
> >
> > - VM_BUG_ON_PAGE(!PageAnon(page), page);
> > + /*
> > + * Check if we have dealt with the compount page
>
> s/compount/compound
Thanks.
> > + * already
> > + */
> > + list_for_each_entry(p, &compound_pagelist, lru) {
> > + if (page == p)
> > + break;
> > + }
> > + if (page == p)
> > + continue;
>
> I don't quite understand why we need the above check. My understanding
> is when we scan the ptes, once the first PTE mapped subpage is found,
> then the THP would be added into compound_pagelist, then the later
> loop would find the same THP on the list then just break the loop. Did
> I miss anything?
We skip the iteration and look at the next pte. We've already isolated the
page. Nothing to do here.
> > + }
> >
> > /*
> > * We can do it before isolate_lru_page because the
> > @@ -640,6 +662,9 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> > page_is_young(page) || PageReferenced(page) ||
> > mmu_notifier_test_young(vma->vm_mm, address))
> > referenced++;
> > +
> > + if (PageCompound(page))
> > + list_add_tail(&page->lru, &compound_pagelist);
> > }
> > if (likely(writable)) {
> > if (likely(referenced)) {
> > @@ -1185,11 +1210,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
> > goto out_unmap;
> > }
> >
> > - /* TODO: teach khugepaged to collapse THP mapped with pte */
> > - if (PageCompound(page)) {
> > - result = SCAN_PAGE_COMPOUND;
> > - goto out_unmap;
> > - }
> > + page = compound_head(page);
> >
> > /*
> > * Record which node the original page is from and save this
> > --
> > 2.26.0
> >
> >
--
Kirill A. Shutemov
next prev parent reply other threads:[~2020-03-28 0:34 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-27 17:05 [PATCH 0/7] thp/khugepaged improvements and CoW semantics Kirill A. Shutemov
2020-03-27 17:05 ` [PATCH 1/7] khugepaged: Add self test Kirill A. Shutemov
2020-03-27 17:05 ` [PATCH 2/7] khugepaged: Do not stop collapse if less than half PTEs are referenced Kirill A. Shutemov
2020-03-27 17:30 ` Zi Yan
2020-03-27 17:46 ` Yang Shi
2020-03-27 17:05 ` [PATCH 3/7] khugepaged: Drain LRU add pagevec to get rid of extra pins Kirill A. Shutemov
2020-03-27 17:34 ` Zi Yan
2020-03-28 0:20 ` Kirill A. Shutemov
2020-03-27 18:10 ` Yang Shi
2020-03-28 12:18 ` Kirill A. Shutemov
2020-03-30 18:30 ` Yang Shi
2020-03-30 21:38 ` Kirill A. Shutemov
2020-03-27 17:05 ` [PATCH 4/7] khugepaged: Allow to callapse a page shared across fork Kirill A. Shutemov
2020-03-27 18:19 ` Zi Yan
2020-03-27 21:31 ` Yang Shi
2020-03-27 21:44 ` Zi Yan
2020-03-27 17:05 ` [PATCH 5/7] khugepaged: Allow to collapse PTE-mapped compound pages Kirill A. Shutemov
2020-03-27 18:53 ` Yang Shi
2020-03-28 0:34 ` Kirill A. Shutemov [this message]
2020-03-28 1:09 ` Yang Shi
2020-03-28 12:27 ` Kirill A. Shutemov
2020-03-30 18:38 ` Yang Shi
2020-03-27 18:55 ` Zi Yan
2020-03-28 0:39 ` Kirill A. Shutemov
2020-03-28 1:17 ` Zi Yan
2020-03-28 12:33 ` Kirill A. Shutemov
2020-03-30 18:41 ` Yang Shi
2020-03-30 18:50 ` Yang Shi
2020-03-31 14:08 ` Kirill A. Shutemov
2020-04-01 19:45 ` Yang Shi
2020-03-27 20:45 ` Yang Shi
2020-03-28 0:40 ` Kirill A. Shutemov
2020-03-28 1:12 ` Yang Shi
2020-03-27 17:06 ` [PATCH 6/7] thp: Change CoW semantics for anon-THP Kirill A. Shutemov
2020-03-27 20:07 ` Yang Shi
2020-03-28 0:43 ` Kirill A. Shutemov
2020-03-28 1:30 ` Yang Shi
2020-03-27 17:06 ` [PATCH 7/7] khugepaged: Introduce 'max_ptes_shared' tunable Kirill A. Shutemov
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