From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
Zi Yan <zi.yan@sent.com>,
mgorman@techsingularity.net, riel@redhat.com
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kirill.shutemov@linux.intel.com, akpm@linux-foundation.org,
minchan@kernel.org, vbabka@suse.cz, n-horiguchi@ah.jp.nec.com,
khandual@linux.vnet.ibm.com, zi.yan@cs.rutgers.edu,
Zi Yan <ziy@nvidia.com>
Subject: Re: [PATCH v3 03/14] mm: use pmd lock instead of racy checks in zap_pmd_range()
Date: Tue, 07 Feb 2017 19:25:30 +0530 [thread overview]
Message-ID: <87bmueqf59.fsf@skywalker.in.ibm.com> (raw)
In-Reply-To: <20170206160751.GA29962@node.shutemov.name>
"Kirill A. Shutemov" <kirill@shutemov.name> writes:
> On Sun, Feb 05, 2017 at 11:12:41AM -0500, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> Originally, zap_pmd_range() checks pmd value without taking pmd lock.
>> This can cause pmd_protnone entry not being freed.
>>
>> Because there are two steps in changing a pmd entry to a pmd_protnone
>> entry. First, the pmd entry is cleared to a pmd_none entry, then,
>> the pmd_none entry is changed into a pmd_protnone entry.
>> The racy check, even with barrier, might only see the pmd_none entry
>> in zap_pmd_range(), thus, the mapping is neither split nor zapped.
>
> That's definately a good catch.
>
> But I don't agree with the solution. Taking pmd lock on each
> zap_pmd_range() is a significant hit by scalability of the code path.
> Yes, split ptl lock helps, but it would be nice to avoid the lock in first
> place.
>
> Can we fix change_huge_pmd() instead? Is there a reason why we cannot
> setup the pmd_protnone() atomically?
>
> Mel? Rik?
>
I am also trying to fixup the usage of set_pte_at on ptes that are
valid/present (that this autonuma ptes). I guess what we are missing is a
variant of pte update routines that can atomically update a pte without
clearing it and that also doesn't do a tlb flush ?
-aneesh
next prev parent reply other threads:[~2017-02-07 13:56 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-05 16:12 [PATCH v3 00/14] mm: page migration enhancement for thp Zi Yan
2017-02-05 16:12 ` [PATCH v3 01/14] mm: thp: make __split_huge_pmd_locked visible Zi Yan
2017-02-06 6:12 ` Naoya Horiguchi
2017-02-06 12:10 ` Zi Yan
2017-02-06 15:02 ` Matthew Wilcox
2017-02-06 15:03 ` Zi Yan
2017-02-05 16:12 ` [PATCH v3 02/14] mm: thp: create new __zap_huge_pmd_locked function Zi Yan
2017-02-05 16:12 ` [PATCH v3 03/14] mm: use pmd lock instead of racy checks in zap_pmd_range() Zi Yan
2017-02-06 4:02 ` Hillf Danton
2017-02-06 4:14 ` Zi Yan
2017-02-06 7:43 ` Naoya Horiguchi
2017-02-06 13:02 ` Zi Yan
2017-02-06 23:22 ` Naoya Horiguchi
2017-02-06 16:07 ` Kirill A. Shutemov
2017-02-06 16:32 ` Zi Yan
2017-02-06 17:35 ` Kirill A. Shutemov
2017-02-07 13:55 ` Aneesh Kumar K.V [this message]
2017-02-07 14:19 ` Kirill A. Shutemov
2017-02-07 15:11 ` Zi Yan
2017-02-07 16:37 ` Kirill A. Shutemov
2017-02-07 17:14 ` Zi Yan
2017-02-07 17:45 ` Kirill A. Shutemov
2017-02-13 0:25 ` Zi Yan
2017-02-13 10:59 ` Kirill A. Shutemov
2017-02-13 14:40 ` Andrea Arcangeli
2017-02-05 16:12 ` [PATCH v3 04/14] mm: x86: move _PAGE_SWP_SOFT_DIRTY from bit 7 to bit 1 Zi Yan
2017-02-09 9:14 ` Naoya Horiguchi
2017-02-09 15:07 ` Zi Yan
2017-02-05 16:12 ` [PATCH v3 05/14] mm: mempolicy: add queue_pages_node_check() Zi Yan
2017-02-05 16:12 ` [PATCH v3 06/14] mm: thp: introduce separate TTU flag for thp freezing Zi Yan
2017-02-05 16:12 ` [PATCH v3 07/14] mm: thp: introduce CONFIG_ARCH_ENABLE_THP_MIGRATION Zi Yan
2017-02-05 16:12 ` [PATCH v3 08/14] mm: thp: enable thp migration in generic path Zi Yan
2017-02-09 9:15 ` Naoya Horiguchi
2017-02-09 15:17 ` Zi Yan
2017-02-09 23:04 ` Naoya Horiguchi
2017-02-14 20:13 ` Zi Yan
2017-02-05 16:12 ` [PATCH v3 09/14] mm: thp: check pmd migration entry in common path Zi Yan
2017-02-09 9:16 ` Naoya Horiguchi
2017-02-09 17:36 ` Zi Yan
2017-02-05 16:12 ` [PATCH v3 10/14] mm: soft-dirty: keep soft-dirty bits over thp migration Zi Yan
2017-02-05 16:12 ` [PATCH v3 11/14] mm: hwpoison: soft offline supports " Zi Yan
2017-02-05 16:12 ` [PATCH v3 12/14] mm: mempolicy: mbind and migrate_pages support " Zi Yan
2017-02-05 16:12 ` [PATCH v3 13/14] mm: migrate: move_pages() supports " Zi Yan
2017-02-09 9:16 ` Naoya Horiguchi
2017-02-09 17:37 ` Zi Yan
2017-02-05 16:12 ` [PATCH v3 14/14] mm: memory_hotplug: memory hotremove " Zi Yan
2017-02-23 16:12 ` [PATCH v3 00/14] mm: page migration enhancement for thp Zi Yan
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