linux-kernel - [PATCH] mm,do_huge_pmd_numa_page: remove unnecessary TLB flushing code

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Date:   Tue, 20 Jul 2021 14:55:29 +0800
From:   Huang Ying <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>,
        Yang Shi <shy828301@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Mel Gorman <mgorman@...e.de>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, Zi Yan <ziy@...dia.com>
Subject: [PATCH] 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.

Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Cc: Yang Shi <shy828301@...il.com>
Cc: Dan Carpenter <dan.carpenter@...cle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Vasily Gorbik <gor@...ux.ibm.com>
Cc: Zi Yan <ziy@...dia.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