[PATCH 7/8] mm: remove the extra ZONE_DEVICE struct page refcount
Christoph Hellwig
hch at lst.de
Mon Feb 7 06:32:48 UTC 2022
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 at nvidia.com>.
Signed-off-by: Christoph Hellwig <hch at lst.de>
---
arch/powerpc/kvm/book3s_hv_uvmem.c | 1 -
drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 1 -
drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 -
fs/Kconfig | 1 -
include/linux/memremap.h | 12 +++--
include/linux/mm.h | 6 +--
lib/test_hmm.c | 1 -
mm/Kconfig | 4 --
mm/internal.h | 2 +
mm/memcontrol.c | 11 ++---
mm/memremap.c | 57 ++++++++----------------
mm/migrate.c | 6 ---
mm/swap.c | 16 ++-----
13 files changed, 36 insertions(+), 83 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index e414ca44839fd1..8b6438fa18fc2b 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -712,7 +712,6 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
dpage = pfn_to_page(uvmem_pfn);
dpage->zone_device_data = pvt;
- get_page(dpage);
lock_page(dpage);
return dpage;
out_clear:
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
index cb835f95a76e66..e27ca375876230 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
@@ -225,7 +225,6 @@ svm_migrate_get_vram_page(struct svm_range *prange, unsigned long pfn)
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);
}
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index a5cdfbe32b5e54..7ba66ad68a8a1e 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -326,7 +326,6 @@ nouveau_dmem_page_alloc_locked(struct nouveau_drm *drm)
return NULL;
}
- get_page(page);
lock_page(page);
return page;
}
diff --git a/fs/Kconfig b/fs/Kconfig
index 7a2b11c0b8036d..05efea674bffa0 100644
--- a/fs/Kconfig
+++ b/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
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 514ab46f597e5c..d6a114dd5ea8b7 100644
--- a/include/linux/memremap.h
+++ b/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_vmemmap_nr(struct dev_pagemap *pgmap)
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;
}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80fccfe31c3444..ff9f149ca2017e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1090,7 +1090,7 @@ static inline bool is_zone_movable_page(const struct page *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);
@@ -1103,12 +1103,12 @@ static inline bool put_devmap_managed_page(struct page *page)
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) \
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index e5fc14ba71f33e..cfe63204783918 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -566,7 +566,6 @@ static struct page *dmirror_devmem_alloc_page(struct dmirror_device *mdevice)
}
dpage->zone_device_data = rpage;
- get_page(dpage);
lock_page(dpage);
return dpage;
diff --git a/mm/Kconfig b/mm/Kconfig
index 3326ee3903f330..a1901ae6d06293 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -776,9 +776,6 @@ 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.
@@ -790,7 +787,6 @@ 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
diff --git a/mm/internal.h b/mm/internal.h
index d80300392a194f..a67222d17e5987 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -718,4 +718,6 @@ void vunmap_range_noflush(unsigned long start, unsigned long end);
int numa_migrate_prep(struct page *page, struct vm_area_struct *vma,
unsigned long addr, int page_nid, int *flags);
+void free_zone_device_page(struct page *page);
+
#endif /* __MM_INTERNAL_H */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 09d342c7cbd0d9..d1e97a54ae535e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5503,17 +5503,12 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
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;
}
diff --git a/mm/memremap.c b/mm/memremap.c
index a0ece2344c2cab..fef5734d5e4933 100644
--- a/mm/memremap.c
+++ b/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(struct dev_pagemap *pgmap)
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)
{
@@ -102,23 +101,12 @@ static unsigned long pfn_end(struct dev_pagemap *pgmap, int range_id)
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) -
pfn_first(pgmap, range_id)) >> pgmap->vmemmap_shift;
}
-#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];
@@ -147,13 +135,11 @@ static void pageunmap_range(struct dev_pagemap *pgmap, int range_id)
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);
@@ -464,14 +450,10 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
}
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);
@@ -500,28 +482,27 @@ void free_devmap_managed_page(struct page *page)
*/
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 */
diff --git a/mm/migrate.c b/mm/migrate.c
index c7da064b4781b8..8e0370a73f8a43 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -341,14 +341,8 @@ static int expected_page_refs(struct address_space *mapping, struct page *page)
{
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;
}
diff --git a/mm/swap.c b/mm/swap.c
index 25b55c56614311..c84d6817043257 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -114,17 +114,9 @@ static void __put_compound_page(struct page *page)
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, int nr)
if (put_devmap_managed_page(page))
continue;
if (put_page_testzero(page))
- put_dev_pagemap(page->pgmap);
+ free_zone_device_page(page);
continue;
}
--
2.30.2
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