From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alistair Popple <apopple@nvidia.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Christoph Hellwig <hch@lst.de>, Yang Shi <shy828301@gmail.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Shakeel Butt <shakeelb@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/4] mm/rmap: fix old bug: munlocking THP missed other mlocks
Date: Thu, 8 Jul 2021 16:58:11 +0300 [thread overview]
Message-ID: <20210708135811.775drqgwkwc76vcb@box.shutemov.name> (raw)
In-Reply-To: <cfa154c-d595-406-eb7d-eb9df730f944@google.com>
On Wed, Jul 07, 2021 at 01:08:53PM -0700, Hugh Dickins wrote:
> The kernel recovers in due course from missing Mlocked pages: but there
> was no point in calling page_mlock() (formerly known as try_to_munlock())
> on a THP, because nothing got done even when it was found to be mapped in
> another VM_LOCKED vma.
>
> It's true that we need to be careful: Mlocked accounting of pte-mapped
> THPs is too difficult (so consistently avoided); but Mlocked accounting
> of only-pmd-mapped THPs is supposed to work, even when multiple mappings
> are mlocked and munlocked or munmapped. Refine the tests.
Well, that's true that it should be fine to mlock only-pmd-mapped THPs,
but the refined check doesn't gurantee that the page is not mapped with
PTEs. !PageDoubleMap(page) only guarantees that the page in not mapped
with both PMDs and PTEs at the same time. For anon pages, we clear the
flag when the last PMD mapping is gone and only PTEs left.
Do I miss some detail here? Maybe we exclude anon pages here somehow?
I don't see it.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2021-07-08 13:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-07 20:06 [PATCH 1/4] mm/rmap: fix comments left over from recent changes Hugh Dickins
2021-07-07 20:08 ` [PATCH 2/4] mm/rmap: fix old bug: munlocking THP missed other mlocks Hugh Dickins
2021-07-07 20:53 ` Shakeel Butt
2021-07-08 13:58 ` Kirill A. Shutemov [this message]
2021-07-09 2:50 ` Hugh Dickins
2021-07-09 10:56 ` Kirill A. Shutemov
2021-07-07 20:11 ` [PATCH 3/4] mm/rmap: fix new bug: premature return from page_mlock_one() Hugh Dickins
2021-07-07 20:22 ` Shakeel Butt
2021-07-07 23:14 ` Alistair Popple
2021-07-07 20:13 ` [PATCH 4/4] mm/rmap: try_to_migrate() skip zone_device !device_private Hugh Dickins
2021-07-07 20:54 ` Shakeel Butt
2021-07-07 23:25 ` Alistair Popple
2021-07-07 20:22 ` [PATCH 1/4] mm/rmap: fix comments left over from recent changes Shakeel Butt
2021-07-07 21:26 ` Yang Shi
2021-07-07 21:29 ` Yang Shi
2021-07-07 23:34 ` Alistair Popple
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