The patch titled
Subject: mm: remove the extra ZONE_DEVICE struct page refcount
has been added to the -mm tree. Its filename is
mm-remove-the-extra-zone_device-struct-page-refcount.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-remove-the-extra-zone_device-struct-page-refcount.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-remove-the-extra-zone_device-struct-page-refcount.patch
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------------------------------------------------------
From: Christoph Hellwig <hch@xxxxxx>
Subject: mm: remove the extra ZONE_DEVICE struct page refcount
ZONE_DEVICE struct pages have an extra reference count that complicates
the code for put_page() and several places in the kernel that need to
check the reference count to see that a page is not being used (gup,
compaction, migration, etc.). Clean up the code so the reference count
doesn't need to be treated specially for ZONE_DEVICE pages.
Note that this excludes the special idle page wakeup for fsdax pages,
which still happens at refcount 1. This is a separate issue and will
be sorted out later. Given that only fsdax pages require the
notifiacation when the refcount hits 1 now, the PAGEMAP_OPS Kconfig
symbol can go away and be replaced with a FS_DAX check for this hook
in the put_page fastpath.
Based on an earlier patch from Ralph Campbell <rcampbell@xxxxxxxxxx>.
Link: https://lkml.kernel.org/r/20220210072828.2930359-8-hch@xxxxxx
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Reviewed-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Acked-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Tested-by: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
Cc: Chaitanya Kulkarni <kch@xxxxxxxxxx>
Cc: Christian Knig <christian.koenig@xxxxxxx>
Cc: Karol Herbst <kherbst@xxxxxxxxxx>
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: "Pan, Xinhui" <Xinhui.Pan@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -712,7 +712,6 @@ static struct page *kvmppc_uvmem_get_pag
dpage = pfn_to_page(uvmem_pfn);
dpage->zone_device_data = pvt;
- get_page(dpage);
lock_page(dpage);
return dpage;
out_clear:
--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
@@ -225,7 +225,6 @@ svm_migrate_get_vram_page(struct svm_ran
page = pfn_to_page(pfn);
svm_range_bo_ref(prange->svm_bo);
page->zone_device_data = prange->svm_bo;
- get_page(page);
lock_page(page);
}
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -326,7 +326,6 @@ nouveau_dmem_page_alloc_locked(struct no
return NULL;
}
- get_page(page);
lock_page(page);
return page;
}
--- a/fs/Kconfig~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/fs/Kconfig
@@ -48,7 +48,6 @@ config FS_DAX
bool "File system based Direct Access (DAX) support"
depends on MMU
depends on !(ARM || MIPS || SPARC)
- select DEV_PAGEMAP_OPS if (ZONE_DEVICE && !FS_DAX_LIMITED)
select FS_IOMAP
select DAX
help
--- a/include/linux/memremap.h~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/include/linux/memremap.h
@@ -68,9 +68,9 @@ enum memory_type {
struct dev_pagemap_ops {
/*
- * Called once the page refcount reaches 1. (ZONE_DEVICE pages never
- * reach 0 refcount unless there is a refcount bug. This allows the
- * device driver to implement its own memory management.)
+ * Called once the page refcount reaches 0. The reference count will be
+ * reset to one by the core code after the method is called to prepare
+ * for handing out the page again.
*/
void (*page_free)(struct page *page);
@@ -133,16 +133,14 @@ static inline unsigned long pgmap_vmemma
static inline bool is_device_private_page(const struct page *page)
{
- return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
- IS_ENABLED(CONFIG_DEVICE_PRIVATE) &&
+ return IS_ENABLED(CONFIG_DEVICE_PRIVATE) &&
is_zone_device_page(page) &&
page->pgmap->type == MEMORY_DEVICE_PRIVATE;
}
static inline bool is_pci_p2pdma_page(const struct page *page)
{
- return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
- IS_ENABLED(CONFIG_PCI_P2PDMA) &&
+ return IS_ENABLED(CONFIG_PCI_P2PDMA) &&
is_zone_device_page(page) &&
page->pgmap->type == MEMORY_DEVICE_PCI_P2PDMA;
}
--- a/include/linux/mm.h~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/include/linux/mm.h
@@ -1085,7 +1085,7 @@ static inline bool is_zone_movable_page(
return page_zonenum(page) == ZONE_MOVABLE;
}
-#ifdef CONFIG_DEV_PAGEMAP_OPS
+#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_FS_DAX)
DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
bool __put_devmap_managed_page(struct page *page);
@@ -1098,12 +1098,12 @@ static inline bool put_devmap_managed_pa
return __put_devmap_managed_page(page);
}
-#else /* CONFIG_DEV_PAGEMAP_OPS */
+#else /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
static inline bool put_devmap_managed_page(struct page *page)
{
return false;
}
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
+#endif /* CONFIG_ZONE_DEVICE && CONFIG_FS_DAX */
/* 127: arbitrary random number, small enough to assemble well */
#define folio_ref_zero_or_close_to_overflow(folio) \
--- a/lib/test_hmm.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/lib/test_hmm.c
@@ -566,7 +566,6 @@ static struct page *dmirror_devmem_alloc
}
dpage->zone_device_data = rpage;
- get_page(dpage);
lock_page(dpage);
return dpage;
--- a/mm/internal.h~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/mm/internal.h
@@ -717,4 +717,6 @@ int numa_migrate_prep(struct page *page,
DECLARE_PER_CPU(struct per_cpu_nodestat, boot_nodestats);
+void free_zone_device_page(struct page *page);
+
#endif /* __MM_INTERNAL_H */
--- a/mm/Kconfig~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/mm/Kconfig
@@ -782,9 +782,6 @@ config ZONE_DEVICE
If FS_DAX is enabled, then say Y.
-config DEV_PAGEMAP_OPS
- bool
-
#
# Helpers to mirror range of the CPU page tables of a process into device page
# tables.
@@ -796,7 +793,6 @@ config HMM_MIRROR
config DEVICE_PRIVATE
bool "Unaddressable device memory (GPU memory, ...)"
depends on ZONE_DEVICE
- select DEV_PAGEMAP_OPS
help
Allows creation of struct pages to represent unaddressable device
--- a/mm/memcontrol.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/mm/memcontrol.c
@@ -5506,17 +5506,12 @@ static struct page *mc_handle_swap_pte(s
return NULL;
/*
- * Handle MEMORY_DEVICE_PRIVATE which are ZONE_DEVICE page belonging to
- * a device and because they are not accessible by CPU they are store
- * as special swap entry in the CPU page table.
+ * Handle device private pages that are not accessible by the CPU, but
+ * stored as special swap entries in the page table.
*/
if (is_device_private_entry(ent)) {
page = pfn_swap_entry_to_page(ent);
- /*
- * MEMORY_DEVICE_PRIVATE means ZONE_DEVICE page and which have
- * a refcount of 1 when free (unlike normal page)
- */
- if (!page_ref_add_unless(page, 1, 1))
+ if (!get_page_unless_zero(page))
return NULL;
return page;
}
--- a/mm/memremap.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/mm/memremap.c
@@ -12,6 +12,7 @@
#include <linux/types.h>
#include <linux/wait_bit.h>
#include <linux/xarray.h>
+#include "internal.h"
static DEFINE_XARRAY(pgmap_array);
@@ -37,21 +38,19 @@ unsigned long memremap_compat_align(void
EXPORT_SYMBOL_GPL(memremap_compat_align);
#endif
-#ifdef CONFIG_DEV_PAGEMAP_OPS
+#ifdef CONFIG_FS_DAX
DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
EXPORT_SYMBOL(devmap_managed_key);
static void devmap_managed_enable_put(struct dev_pagemap *pgmap)
{
- if (pgmap->type == MEMORY_DEVICE_PRIVATE ||
- pgmap->type == MEMORY_DEVICE_FS_DAX)
+ if (pgmap->type == MEMORY_DEVICE_FS_DAX)
static_branch_dec(&devmap_managed_key);
}
static void devmap_managed_enable_get(struct dev_pagemap *pgmap)
{
- if (pgmap->type == MEMORY_DEVICE_PRIVATE ||
- pgmap->type == MEMORY_DEVICE_FS_DAX)
+ if (pgmap->type == MEMORY_DEVICE_FS_DAX)
static_branch_inc(&devmap_managed_key);
}
#else
@@ -61,7 +60,7 @@ static void devmap_managed_enable_get(st
static void devmap_managed_enable_put(struct dev_pagemap *pgmap)
{
}
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
+#endif /* CONFIG_FS_DAX */
static void pgmap_array_delete(struct range *range)
{
@@ -102,13 +101,6 @@ static unsigned long pfn_end(struct dev_
return (range->start + range_len(range)) >> PAGE_SHIFT;
}
-static unsigned long pfn_next(struct dev_pagemap *pgmap, unsigned long pfn)
-{
- if (pfn % (1024 << pgmap->vmemmap_shift))
- cond_resched();
- return pfn + pgmap_vmemmap_nr(pgmap);
-}
-
static unsigned long pfn_len(struct dev_pagemap *pgmap, unsigned long range_id)
{
return (pfn_end(pgmap, range_id) -
@@ -135,10 +127,6 @@ bool pfn_zone_device_reserved(unsigned l
return ret;
}
-#define for_each_device_pfn(pfn, map, i) \
- for (pfn = pfn_first(map, i); pfn < pfn_end(map, i); \
- pfn = pfn_next(map, pfn))
-
static void pageunmap_range(struct dev_pagemap *pgmap, int range_id)
{
struct range *range = &pgmap->ranges[range_id];
@@ -167,13 +155,11 @@ static void pageunmap_range(struct dev_p
void memunmap_pages(struct dev_pagemap *pgmap)
{
- unsigned long pfn;
int i;
percpu_ref_kill(&pgmap->ref);
for (i = 0; i < pgmap->nr_range; i++)
- for_each_device_pfn(pfn, pgmap, i)
- put_page(pfn_to_page(pfn));
+ percpu_ref_put_many(&pgmap->ref, pfn_len(pgmap, i));
wait_for_completion(&pgmap->done);
percpu_ref_exit(&pgmap->ref);
@@ -485,14 +471,10 @@ struct dev_pagemap *get_dev_pagemap(unsi
}
EXPORT_SYMBOL_GPL(get_dev_pagemap);
-#ifdef CONFIG_DEV_PAGEMAP_OPS
-void free_devmap_managed_page(struct page *page)
+void free_zone_device_page(struct page *page)
{
- /* notify page idle for dax */
- if (!is_device_private_page(page)) {
- wake_up_var(&page->_refcount);
+ if (WARN_ON_ONCE(!is_device_private_page(page)))
return;
- }
__ClearPageWaiters(page);
@@ -521,28 +503,27 @@ void free_devmap_managed_page(struct pag
*/
page->mapping = NULL;
page->pgmap->ops->page_free(page);
+
+ /*
+ * Reset the page count to 1 to prepare for handing out the page again.
+ */
+ set_page_count(page, 1);
}
+#ifdef CONFIG_FS_DAX
bool __put_devmap_managed_page(struct page *page)
{
- if (page->pgmap->type != MEMORY_DEVICE_PRIVATE &&
- page->pgmap->type != MEMORY_DEVICE_FS_DAX)
+ if (page->pgmap->type != MEMORY_DEVICE_FS_DAX)
return false;
/*
- * devmap page refcounts are 1-based, rather than 0-based: if
+ * fsdax page refcounts are 1-based, rather than 0-based: if
* refcount is 1, then the page is free and the refcount is
* stable because nobody holds a reference on the page.
*/
- switch (page_ref_dec_return(page)) {
- case 1:
- free_devmap_managed_page(page);
- break;
- case 0:
- __put_page(page);
- break;
- }
+ if (page_ref_dec_return(page) == 1)
+ wake_up_var(&page->_refcount);
return true;
}
EXPORT_SYMBOL(__put_devmap_managed_page);
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
+#endif /* CONFIG_FS_DAX */
--- a/mm/migrate.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/mm/migrate.c
@@ -341,14 +341,8 @@ static int expected_page_refs(struct add
{
int expected_count = 1;
- /*
- * Device private pages have an extra refcount as they are
- * ZONE_DEVICE pages.
- */
- expected_count += is_device_private_page(page);
if (mapping)
expected_count += compound_nr(page) + page_has_private(page);
-
return expected_count;
}
--- a/mm/swap.c~mm-remove-the-extra-zone_device-struct-page-refcount
+++ a/mm/swap.c
@@ -122,17 +122,9 @@ static void __put_compound_page(struct p
void __put_page(struct page *page)
{
- if (is_zone_device_page(page)) {
- put_dev_pagemap(page->pgmap);
-
- /*
- * The page belongs to the device that created pgmap. Do
- * not return it to page allocator.
- */
- return;
- }
-
- if (unlikely(PageCompound(page)))
+ if (unlikely(is_zone_device_page(page)))
+ free_zone_device_page(page);
+ else if (unlikely(PageCompound(page)))
__put_compound_page(page);
else
__put_single_page(page);
@@ -933,7 +925,7 @@ void release_pages(struct page **pages,
if (put_devmap_managed_page(page))
continue;
if (put_page_testzero(page))
- put_dev_pagemap(page->pgmap);
+ free_zone_device_page(page);
continue;
}
_
Patches currently in -mm which might be from hch@xxxxxx are
mm-unexport-page_init_poison.patch
mm-remove-a-pointless-config_zone_device-check-in-memremap_pages.patch
mm-remove-the-__kernel__-guard-from-linux-mmh.patch
mm-remove-pointless-includes-from-linux-hmmh.patch
mm-move-free_devmap_managed_page-to-memremapc.patch
mm-simplify-freeing-of-devmap-managed-pages.patch
mm-dont-include-linux-memremaph-in-linux-mmh.patch
mm-remove-the-extra-zone_device-struct-page-refcount.patch
fsdax-depend-on-zone_device-fs_dax_limited.patch
mm-generalize-the-pgmap-based-page_free-infrastructure.patch
mm-refactor-check_and_migrate_movable_pages.patch
mm-refactor-the-zone_device-handling-in-migrate_vma_insert_page.patch
mm-refactor-the-zone_device-handling-in-migrate_vma_pages.patch
mm-move-the-migrate_vma_-device-migration-code-into-its-own-file.patch
mm-build-migrate_vma_-for-all-configs-with-zone_device-support.patch
mm-add-zone-device-coherent-type-memory-support.patch
mm-add-device-coherent-vma-selection-for-memory-migration.patch
