The patch titled
Subject: mm/gup: do not migrate zero page
has been added to the -mm tree. Its filename is
mm-gup-do-not-migrate-zero-page.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-gup-do-not-migrate-zero-page.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-do-not-migrate-zero-page.patch
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------------------------------------------------------
From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: mm/gup: do not migrate zero page
On some platforms ZERO_PAGE(0) might end-up in a movable zone. Do not
migrate zero page in gup during longterm pinning as migration of zero page
is not allowed.
For example, in x86 QEMU with 16G of memory and kernelcore=5G parameter, I
see the following:
Boot#1: zero_pfn 0x48a8d zero_pfn zone: ZONE_DMA32
Boot#2: zero_pfn 0x20168d zero_pfn zone: ZONE_MOVABLE
On x86, empty_zero_page is declared in .bss and depending on the loader
may end up in different physical locations during boots.
Also, move is_zero_pfn() my_zero_pfn() functions under CONFIG_MMU, because
zero_pfn that they are using is declared in memory.c which is compiled
with CONFIG_MMU.
Link: https://lkml.kernel.org/r/20210201153827.444374-9-pasha.tatashin@xxxxxxxxxx
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 3 ++-
include/linux/mmzone.h | 4 ++++
include/linux/pgtable.h | 3 +--
3 files changed, 7 insertions(+), 3 deletions(-)
--- a/include/linux/mm.h~mm-gup-do-not-migrate-zero-page
+++ a/include/linux/mm.h
@@ -1124,7 +1124,8 @@ static inline bool is_zone_movable_page(
/* MIGRATE_CMA and ZONE_MOVABLE do not allow pin pages */
static inline bool is_pinnable_page(struct page *page)
{
- return !is_zone_movable_page(page) && !is_migrate_cma_page(page);
+ return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) ||
+ is_zero_pfn(page_to_pfn(page));
}
#ifdef CONFIG_DEV_PAGEMAP_OPS
--- a/include/linux/mmzone.h~mm-gup-do-not-migrate-zero-page
+++ a/include/linux/mmzone.h
@@ -407,6 +407,10 @@ enum zone_type {
* techniques might use alloc_contig_range() to hide previously
* exposed pages from the buddy again (e.g., to implement some sort
* of memory unplug in virtio-mem).
+ * 6. ZERO_PAGE(0), kernelcore/movablecore setups might create
+ * situations where ZERO_PAGE(0) which is allocated differently
+ * on different platforms may end up in a movable zone. ZERO_PAGE(0)
+ * cannot be migrated.
*
* In general, no unmovable allocations that degrade memory offlining
* should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range())
--- a/include/linux/pgtable.h~mm-gup-do-not-migrate-zero-page
+++ a/include/linux/pgtable.h
@@ -1115,6 +1115,7 @@ extern void untrack_pfn(struct vm_area_s
extern void untrack_pfn_moved(struct vm_area_struct *vma);
#endif
+#ifdef CONFIG_MMU
#ifdef __HAVE_COLOR_ZERO_PAGE
static inline int is_zero_pfn(unsigned long pfn)
{
@@ -1139,8 +1140,6 @@ static inline unsigned long my_zero_pfn(
}
#endif
-#ifdef CONFIG_MMU
-
#ifndef CONFIG_TRANSPARENT_HUGEPAGE
static inline int pmd_trans_huge(pmd_t pmd)
{
_
Patches currently in -mm which might be from pasha.tatashin@xxxxxxxxxx are
mm-gup-dont-pin-migrated-cma-pages-in-movable-zone.patch
mm-gup-check-every-subpage-of-a-compound-page-during-isolation.patch
mm-gup-return-an-error-on-migration-failure.patch
mm-gup-check-for-isolation-errors.patch
mm-cma-rename-pf_memalloc_nocma-to-pf_memalloc_pin.patch
mm-apply-per-task-gfp-constraints-in-fast-path.patch
mm-honor-pf_memalloc_pin-for-all-movable-pages.patch
mm-gup-do-not-migrate-zero-page.patch
mm-gup-migrate-pinned-pages-out-of-movable-zone.patch
memory-hotplugrst-add-a-note-about-zone_movable-and-page-pinning.patch
mm-gup-change-index-type-to-long-as-it-counts-pages.patch
mm-gup-longterm-pin-migration-cleanup.patch
selftests-vm-gup_test-fix-test-flag.patch
selftests-vm-gup_test-test-faulting-in-kernel-and-verify-pinnable-pages.patch
