From: Hugh Dickins <hughd@google.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Zi Yan <ziy@nvidia.com>, Yang Shi <shy828301@gmail.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm/thp: Update mm_struct's MM_ANONPAGES stat for huge zero pages
Date: Thu, 20 May 2021 19:17:04 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.2105201852230.5752@eggly.anvils> (raw)
In-Reply-To: <1621313300-1118-1-git-send-email-anshuman.khandual@arm.com>
On Tue, 18 May 2021, Anshuman Khandual wrote:
> Although the zero huge page is being shared across various processes, each
> mapping needs to update its mm_struct's MM_ANONPAGES stat by HPAGE_PMD_NR
> to be consistent. This just updates the stats in set_huge_zero_page() after
> the mapping gets created and in zap_huge_pmd() when mapping gets destroyed.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
NAK.
For consistency with what? In the all the years that the huge zero page
has existed, it has been intentionally exempted from rss accounting:
consistent with the small zero page, which itself has always been
intentionally exempted from rss accounting. In fact, that's a good part
of the reason the huge zero page was introduced (see 4a6c1297268c).
To change that now will break any users depending on it.
Not to mention the
BUG: Bad rss-counter state mm:00000000aa61ef82 type:MM_ANONPAGES val:512
I just got from mmotm.
Hugh
> ---
> This applies on v5.13-rc2.
>
> Changes in V1:
>
> - Updated MM_ANONPAGES stat in zap_huge_pmd()
> - Updated the commit message
>
> Changes in RFC:
>
> https://lore.kernel.org/linux-mm/1620890438-9127-1-git-send-email-anshuman.khandual@arm.com/
>
> mm/huge_memory.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 63ed6b25deaa..306d0a41bf75 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -706,6 +706,7 @@ static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
> if (pgtable)
> pgtable_trans_huge_deposit(mm, pmd, pgtable);
> set_pmd_at(mm, haddr, pmd, entry);
> + add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
> mm_inc_nr_ptes(mm);
> }
>
> @@ -1678,6 +1679,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
> } else if (is_huge_zero_pmd(orig_pmd)) {
> zap_deposited_table(tlb->mm, pmd);
> + add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
> spin_unlock(ptl);
> tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
> } else {
> --
> 2.20.1
next prev parent reply other threads:[~2021-05-21 2:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-18 4:48 [PATCH] mm/thp: Update mm_struct's MM_ANONPAGES stat for huge zero pages Anshuman Khandual
2021-05-18 14:12 ` Zi Yan
2021-05-21 2:17 ` Hugh Dickins [this message]
2021-05-21 4:18 ` Anshuman Khandual
2021-05-21 5:56 ` Hugh Dickins
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