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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: "Huang, Ying" <ying.huang@intel.com>,
	Sean Christopherson <seanjc@google.com>
Cc: Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Mel Gorman <mgorman@suse.de>,
	Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Hugh Dickins <hughd@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Michal Hocko <mhocko@suse.com>, Vasily Gorbik <gor@linux.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	kvm list <kvm@vger.kernel.org>
Subject: Re: [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code
Date: Thu, 22 Jul 2021 09:36:07 +0200	[thread overview]
Message-ID: <572f1ddd-9ac6-fb09-9a24-1c667dbd1d03@de.ibm.com> (raw)
In-Reply-To: <87lf5z9osl.fsf@yhuang6-desk2.ccr.corp.intel.com>



On 22.07.21 02:26, Huang, Ying wrote:
> Sean Christopherson <seanjc@google.com> writes:
>>>
>>> Thanks, I think you are correct. By looking into commit 7066f0f933a1
>>> ("mm: thp: fix mmu_notifier in migrate_misplaced_transhuge_page()"),
>>> the tlb flush and mmu notifier invalidate were needed since the old
>>> numa fault implementation didn't change PTE to migration entry so it
>>> may cause data corruption due to the writes from GPU secondary MMU.
>>>
>>> The refactor does use the generic migration code which converts PTE to
>>> migration entry before copying data to the new page.
>>
>> That's my understanding as well, based on this blurb from commit 7066f0f933a1.
>>
>>      The standard PAGE_SIZEd migrate_misplaced_page is less accelerated and
>>      uses the generic migrate_pages which transitions the pte from
>>      numa/protnone to a migration entry in try_to_unmap_one() and flushes TLBs
>>      and all mmu notifiers there before copying the page.
>>
>> That analysis/justification for removing the invalidate_range() call should be
>> captured in the changelog.  Confirmation from Andrea would be a nice bonus.
> 
> When we flush CPU TLB for a page that may be shared with device/VM TLB,
> we will call MMU notifiers for the page to flush the device/VM TLB.
> Right?  So when we replaced CPU TLB flushing in do_huge_pmd_numa_page()
> with that in try_to_migrate_one(), we will replace the MMU notifiers
> calling too.  Do you agree?

Can someone write an updated commit messages that contains this information?

  reply	other threads:[~2021-07-22  7:36 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20  6:55 Huang Ying
2021-07-20 13:36 ` Zi Yan
2021-07-20 14:25 ` Christian Borntraeger
2021-07-20 20:53   ` Yang Shi
2021-07-20 21:04     ` Zi Yan
2021-07-20 22:19       ` Yang Shi
2021-07-21 15:41         ` Sean Christopherson
2021-07-22  0:26           ` Huang, Ying
2021-07-22  7:36             ` Christian Borntraeger [this message]
2021-07-22 23:10               ` Huang, Ying
2021-07-23  0:03               ` Huang, Ying
2021-07-23 20:19                 ` Andrew Morton
2021-07-20 20:48 ` Yang Shi
2021-07-20 22:21   ` Yang Shi

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