From: Zi Yan <ziy@nvidia.com>
To: Yang Shi <shy828301@gmail.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
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 4/7] khugepaged: Allow to callapse a page shared across fork
Date: Fri, 27 Mar 2020 17:44:56 -0400 [thread overview]
Message-ID: <2498F20B-DD98-4244-AD60-58D4A771ADF6@nvidia.com> (raw)
In-Reply-To: <CAHbLzkrLxB93xs78xejsBsZ=-b+oqNao6a5Bydi8-6+wpzjKQg@mail.gmail.com>
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<snip>
>>> /*
>>> * Drain pagevec and retry just in case we can get rid
>>> * of the extra pin, like in swapin case.
>>> */
>>> lru_add_drain();
>>> }
>>> - if (page_count(page) != 1 + PageSwapCache(page)) {
>>> + if (total_mapcount(page) + PageSwapCache(page) !=
>>> + page_count(page)) {
>>> unlock_page(page);
>>> result = SCAN_PAGE_COUNT;
>>> goto out;
>>> @@ -680,7 +688,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
>>> } else {
>>> src_page = pte_page(pteval);
>>> copy_user_highpage(page, src_page, address, vma);
>>> - VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
>>
>> Maybe replace it with this?
>>
>> VM_BUG_ON_PAGE(page_mapcount(src_page) + PageSwapCache(src_page) != page_count(src_page), src_page);
>
> I don't think this is correct either. If a THP is PTE mapped its
> refcount would be bumped by the number of PTE mapped subpages. But
> page_mapcount() would just return the mapcount of that specific
> subpage. So, total_mapcount() should be used, but the same check has
> been done before reaching here.
Yes, you are right. Thanks.
Please disregard this comment.
—
Best Regards,
Yan Zi
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next prev parent reply other threads:[~2020-03-27 21:45 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 [this message]
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
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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