From: "Huang, Ying" <ying.huang@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
Sean Christopherson <seanjc@google.com>,
Yang Shi <shy828301@gmail.com>, Zi Yan <ziy@nvidia.com>,
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: Fri, 23 Jul 2021 08:03:42 +0800 [thread overview]
Message-ID: <878s1xaobl.fsf@yhuang6-desk2.ccr.corp.intel.com> (raw)
In-Reply-To: <572f1ddd-9ac6-fb09-9a24-1c667dbd1d03@de.ibm.com> (Christian Borntraeger's message of "Thu, 22 Jul 2021 09:36:07 +0200")
Christian Borntraeger <borntraeger@de.ibm.com> writes:
> 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?
Hi, Andrew,
Can you help to add the following text to the end of the original patch
description?
"
The mmu_notifier_invalidate_range() in do_huge_pmd_numa_page() is
deleted too. Because migrate_pages() takes care of that too when CPU
TLB is flushed.
"
Or, if you prefer the complete patch, it's as below.
Best Regards,
Huang, Ying
------------------------------------8<---------------------------------------------
From a7ce0c58dcc0d2f0d87b43b4e93a6623d78c9c25 Mon Sep 17 00:00:00 2001
From: Huang Ying <ying.huang@intel.com>
Date: Tue, 13 Jul 2021 13:41:37 +0800
Subject: [PATCH -V2] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing
code
Before the commit c5b5a3dd2c1f ("mm: thp: refactor NUMA fault
handling"), the TLB flushing is done in do_huge_pmd_numa_page() itself
via flush_tlb_range().
But after commit c5b5a3dd2c1f ("mm: thp: refactor NUMA fault
handling"), the TLB flushing is done in migrate_pages() as in the
following code path anyway.
do_huge_pmd_numa_page
migrate_misplaced_page
migrate_pages
So now, the TLB flushing code in do_huge_pmd_numa_page() becomes
unnecessary. So the code is deleted in this patch to simplify the
code. This is only code cleanup, there's no visible performance
difference.
The mmu_notifier_invalidate_range() in do_huge_pmd_numa_page() is
deleted too. Because migrate_pages() takes care of that too when CPU
TLB is flushed.
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
---
mm/huge_memory.c | 26 --------------------------
1 file changed, 26 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index afff3ac87067..9f21e44c9030 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1440,32 +1440,6 @@ vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
goto out;
}
- /*
- * Since we took the NUMA fault, we must have observed the !accessible
- * bit. Make sure all other CPUs agree with that, to avoid them
- * modifying the page we're about to migrate.
- *
- * Must be done under PTL such that we'll observe the relevant
- * inc_tlb_flush_pending().
- *
- * We are not sure a pending tlb flush here is for a huge page
- * mapping or not. Hence use the tlb range variant
- */
- if (mm_tlb_flush_pending(vma->vm_mm)) {
- flush_tlb_range(vma, haddr, haddr + HPAGE_PMD_SIZE);
- /*
- * change_huge_pmd() released the pmd lock before
- * invalidating the secondary MMUs sharing the primary
- * MMU pagetables (with ->invalidate_range()). The
- * mmu_notifier_invalidate_range_end() (which
- * internally calls ->invalidate_range()) in
- * change_pmd_range() will run after us, so we can't
- * rely on it here and we need an explicit invalidate.
- */
- mmu_notifier_invalidate_range(vma->vm_mm, haddr,
- haddr + HPAGE_PMD_SIZE);
- }
-
pmd = pmd_modify(oldpmd, vma->vm_page_prot);
page = vm_normal_page_pmd(vma, haddr, pmd);
if (!page)
--
2.30.2
next prev parent reply other threads:[~2021-07-23 0:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-20 6:55 [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code 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
2021-07-22 23:10 ` Huang, Ying
2021-07-23 0:03 ` Huang, Ying [this message]
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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