From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Song Liu <songliubraving@fb.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Matthew Wilcox <matthew.wilcox@oracle.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Kernel Team <Kernel-team@fb.com>,
William Kucharski <william.kucharski@oracle.com>,
"srikar@linux.vnet.ibm.com" <srikar@linux.vnet.ibm.com>
Subject: Re: [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP
Date: Mon, 12 Aug 2019 17:40:45 +0300 [thread overview]
Message-ID: <20190812144045.tkvipsyit3nccvuk@box> (raw)
In-Reply-To: <20190812132257.GB31560@redhat.com>
On Mon, Aug 12, 2019 at 03:22:58PM +0200, Oleg Nesterov wrote:
> On 08/12, Kirill A. Shutemov wrote:
> >
> > On Fri, Aug 09, 2019 at 06:01:18PM +0000, Song Liu wrote:
> > > + if (pte_none(*pte) || !pte_present(*pte))
> > > + continue;
> >
> > You don't need to check both. Present is never none.
>
> Agreed.
>
> Kirill, while you are here, shouldn't retract_page_tables() check
> vma->anon_vma (and probably do mm_find_pmd) under vm_mm->mmap_sem?
>
> Can't it race with, say, do_cow_fault?
vma->anon_vma can race, but it doesn't matter. False-negative is fine.
It's attempt to avoid taking mmap_sem where it can be not productive.
mm_find_pmd() cannot race with do_cow_fault() since the page is locked.
__do_fault() has to return locked page before we touch page tables.
It is somewhat subtle, but I wanted to avoid taking mmap_sem where it is
possible.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2019-08-12 14:40 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-07 23:37 [PATCH v12 0/6] THP aware uprobe Song Liu
2019-08-07 23:37 ` [PATCH v12 1/6] mm: move memcmp_pages() and pages_identical() Song Liu
2019-08-07 23:37 ` [PATCH v12 2/6] uprobe: use original page when all uprobes are removed Song Liu
2019-08-07 23:37 ` [PATCH v12 3/6] mm, thp: introduce FOLL_SPLIT_PMD Song Liu
2019-08-08 16:37 ` Oleg Nesterov
2019-08-08 17:16 ` Song Liu
2019-08-09 16:35 ` Oleg Nesterov
2019-08-09 16:50 ` Song Liu
2019-08-07 23:37 ` [PATCH v12 4/6] uprobe: use FOLL_SPLIT_PMD instead of FOLL_SPLIT Song Liu
2019-08-07 23:37 ` [PATCH v12 5/6] khugepaged: enable collapse pmd for pte-mapped THP Song Liu
2019-08-08 16:33 ` Oleg Nesterov
2019-08-08 17:05 ` Song Liu
2019-08-09 15:24 ` Oleg Nesterov
2019-08-09 16:30 ` Song Liu
2019-08-09 18:01 ` Song Liu
2019-08-12 12:11 ` Kirill A. Shutemov
2019-08-12 13:22 ` Oleg Nesterov
2019-08-12 14:40 ` Kirill A. Shutemov [this message]
2019-08-12 21:04 ` Song Liu
2019-08-13 14:44 ` Song Liu
2019-08-15 10:16 ` Oleg Nesterov
2019-08-15 16:27 ` Song Liu
2019-08-13 13:30 ` Oleg Nesterov
2019-08-13 14:05 ` Oleg Nesterov
2019-08-13 15:05 ` Kirill A. Shutemov
2019-08-13 16:24 ` Oleg Nesterov
2019-08-16 14:54 ` Kirill A. Shutemov
2019-08-12 13:06 ` Oleg Nesterov
2019-08-12 14:36 ` Song Liu
2019-08-07 23:37 ` [PATCH v12 6/6] uprobe: collapse THP pmd after removing all uprobes Song Liu
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