linux-kernel - [PATCH v4 6/6] mm/migrate: remove range invalidation in migrate_vma

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Message-ID: <20200723223004.9586-7-rcampbell@nvidia.com>
Date:   Thu, 23 Jul 2020 15:30:04 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     <linux-rdma@...r.kernel.org>, <linux-mm@...ck.org>,
        <nouveau@...ts.freedesktop.org>, <kvm-ppc@...r.kernel.org>,
        <linux-kselftest@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Jason Gunthorpe <jgg@...lanox.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        "Ben Skeggs" <bskeggs@...hat.com>,
        Bharata B Rao <bharata@...ux.ibm.com>,
        "Ralph Campbell" <rcampbell@...dia.com>
Subject: [PATCH v4 6/6] mm/migrate: remove range invalidation in migrate_vma_pages()

When migrating the special zero page, migrate_vma_pages() calls
mmu_notifier_invalidate_range_start() before replacing the zero page
PFN in the CPU page tables. This is unnecessary since the range was
invalidated in migrate_vma_setup() and the page table entry is checked
to be sure it hasn't changed between migrate_vma_setup() and
migrate_vma_pages(). Therefore, remove the redundant invalidation.
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Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
---
 mm/migrate.c | 20 --------------------
 1 file changed, 20 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 96e1f41a991e..36076ba2f51a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2877,9 +2877,7 @@ void migrate_vma_pages(struct migrate_vma *migrate)
 {
 	const unsigned long npages = migrate->npages;
 	const unsigned long start = migrate->start;
-	struct mmu_notifier_range range;
 	unsigned long addr, i;
-	bool notified = false;
 
 	for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) {
 		struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
@@ -2895,16 +2893,6 @@ void migrate_vma_pages(struct migrate_vma *migrate)
 		if (!page) {
 			if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE))
 				continue;
-			if (!notified) {
-				notified = true;
-
-				mmu_notifier_range_init(&range,
-							MMU_NOTIFY_CLEAR, 0,
-							NULL,
-							migrate->vma->vm_mm,
-							addr, migrate->end);
-				mmu_notifier_invalidate_range_start(&range);
-			}
 			migrate_vma_insert_page(migrate, addr, newpage,
 						&migrate->src[i],
 						&migrate->dst[i]);
@@ -2937,14 +2925,6 @@ void migrate_vma_pages(struct migrate_vma *migrate)
 		if (r != MIGRATEPAGE_SUCCESS)
 			migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
 	}
-
-	/*
-	 * No need to double call mmu_notifier->invalidate_range() callback as
-	 * the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
-	 * did already call it.
-	 */
-	if (notified)
-		mmu_notifier_invalidate_range_only_end(&range);
 }
 EXPORT_SYMBOL(migrate_vma_pages);
 
-- 
2.20.1