linux-ext4 - [PATCH] mm: add device coherent vma selection for memory migration

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Date:   Mon, 31 Jan 2022 13:48:13 -0600
From:   Alex Sierra <alex.sierra@....com>
To:     <akpm@...ux-foundation.org>, <Felix.Kuehling@....com>,
        <linux-mm@...ck.org>, <rcampbell@...dia.com>,
        <linux-ext4@...r.kernel.org>, <linux-xfs@...r.kernel.org>
CC:     <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
        <hch@....de>, <jgg@...dia.com>, <jglisse@...hat.com>,
        <apopple@...dia.com>, <willy@...radead.org>
Subject: [PATCH] mm: add device coherent vma selection for memory migration

This case is used to migrate pages from device memory, back to system
memory. Device coherent type memory is cache coherent from device and CPU
point of view.

Signed-off-by: Alex Sierra <alex.sierra@....com>
Acked-by: Felix Kuehling <Felix.Kuehling@....com>
---
v2:
condition added when migrations from device coherent pages.
---
 include/linux/migrate.h |  1 +
 mm/migrate.c            | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index db96e10eb8da..66a34eae8cb6 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -130,6 +130,7 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
 enum migrate_vma_direction {
 	MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
 	MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
+	MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2,
 };
 
 struct migrate_vma {
diff --git a/mm/migrate.c b/mm/migrate.c
index cd137aedcfe5..69c6830c47c6 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2264,15 +2264,21 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			if (is_writable_device_private_entry(entry))
 				mpfn |= MIGRATE_PFN_WRITE;
 		} else {
-			if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
-				goto next;
 			pfn = pte_pfn(pte);
-			if (is_zero_pfn(pfn)) {
+			if (is_zero_pfn(pfn) &&
+			    (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
 				mpfn = MIGRATE_PFN_MIGRATE;
 				migrate->cpages++;
 				goto next;
 			}
 			page = vm_normal_page(migrate->vma, addr, pte);
+			if (page && !is_zone_device_page(page) &&
+			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
+				goto next;
+			else if (page && is_device_coherent_page(page) &&
+			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
+			     page->pgmap->owner != migrate->pgmap_owner))
+				goto next;
 			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
 			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
 		}
-- 
2.32.0