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Subject[PATCH v8 13/18] mm, dev_pagemap: introduce CONFIG_DEV_PAGEMAP_OPS
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The HMM sub-system extended dev_pagemap to arrange a callback when a
dev_pagemap managed page is freed. Since a dev_pagemap page is free /
idle when its reference count is 1 it requires an additional branch to
check the page-type at put_page() time. Given put_page() is a hot-path
we do not want to incur that check if HMM is not in use, so a static
branch is used to avoid that overhead when not necessary.

Now, the FS_DAX implementation wants to reuse this mechanism for
receiving dev_pagemap ->page_free() callbacks. Rework the HMM-specific
static-key into a generic mechanism that either HMM or FS_DAX code paths
can enable.

For ARCH=um builds, and any other arch that lacks ZONE_DEVICE support,
care must be taken to compile out the DEV_PAGEMAP_OPS infrastructure.
However, we still need to support FS_DAX in the FS_DAX_LIMITED case
implemented by the s390/dcssblk driver.

Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>
Reported-by: Thomas Meyer <thomas@m3y3r.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/dax/super.c | 4 ++-
fs/Kconfig | 1 +
include/linux/dax.h | 35 ++++++++++++++++-------
include/linux/memremap.h | 17 -----------
include/linux/mm.h | 71 ++++++++++++++++++++++++++++++++++------------
kernel/memremap.c | 30 +++++++++++++++++--
mm/Kconfig | 5 +++
mm/hmm.c | 13 +-------
mm/swap.c | 3 +-
9 files changed, 116 insertions(+), 63 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 7d260f118a39..3bafaddd02f1 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -164,7 +164,7 @@ struct dax_device {
const struct dax_operations *ops;
};

-#if IS_ENABLED(CONFIG_FS_DAX)
+#if IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS)
static void generic_dax_pagefree(struct page *page, void *data)
{
/* TODO: wakeup page-idle waiters */
@@ -190,6 +190,7 @@ struct dax_device *fs_dax_claim(struct dax_device *dax_dev, void *owner)
return NULL;
}

+ dev_pagemap_get_ops();
pgmap->type = MEMORY_DEVICE_FS_DAX;
pgmap->page_free = generic_dax_pagefree;
pgmap->data = owner;
@@ -228,6 +229,7 @@ void __fs_dax_release(struct dax_device *dax_dev, void *owner)
pgmap->type = MEMORY_DEVICE_HOST;
pgmap->page_free = NULL;
pgmap->data = NULL;
+ dev_pagemap_put_ops();
mutex_unlock(&devmap_lock);
}
EXPORT_SYMBOL_GPL(__fs_dax_release);
diff --git a/fs/Kconfig b/fs/Kconfig
index bc821a86d965..1e050e012eb9 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -38,6 +38,7 @@ config FS_DAX
bool "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/dax.h b/include/linux/dax.h
index a88ff009e2a1..a36b74aa96e8 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -4,6 +4,7 @@

#include <linux/fs.h>
#include <linux/mm.h>
+#include <linux/genhd.h>
#include <linux/radix-tree.h>
#include <asm/pgtable.h>

@@ -87,12 +88,8 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
return dax_get_by_host(host);
}

-struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner);
-void fs_dax_release(struct dax_device *dax_dev, void *owner);
int dax_writeback_mapping_range(struct address_space *mapping,
struct block_device *bdev, struct writeback_control *wbc);
-struct dax_device *fs_dax_claim(struct dax_device *dax_dev, void *owner);
-void __fs_dax_release(struct dax_device *dax_dev, void *owner);
#else
static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
{
@@ -104,26 +101,42 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
return NULL;
}

+static inline int dax_writeback_mapping_range(struct address_space *mapping,
+ struct block_device *bdev, struct writeback_control *wbc)
+{
+ return -EOPNOTSUPP;
+}
+#endif
+
+#if IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS)
+struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner);
+struct dax_device *fs_dax_claim(struct dax_device *dax_dev, void *owner);
+void __fs_dax_release(struct dax_device *dax_dev, void *owner);
+void fs_dax_release(struct dax_device *dax_dev, void *owner);
+#else
+#ifdef CONFIG_BLOCK
static inline struct dax_device *fs_dax_claim_bdev(struct block_device *bdev,
void *owner)
{
- return NULL;
+ return fs_dax_get_by_host(bdev->bd_disk->disk_name);
}
-
-static inline void fs_dax_release(struct dax_device *dax_dev, void *owner)
+#else
+static inline struct dax_device *fs_dax_claim_bdev(struct block_device *bdev,
+ void *owner)
{
+ return NULL;
}
+#endif

-static inline int dax_writeback_mapping_range(struct address_space *mapping,
- struct block_device *bdev, struct writeback_control *wbc)
+static inline void fs_dax_release(struct dax_device *dax_dev, void *owner)
{
- return -EOPNOTSUPP;
+ put_dax(dax_dev);
}

static inline struct dax_device *fs_dax_claim(struct dax_device *dax_dev,
void *owner)
{
- return NULL;
+ return dax_dev;
}

static inline void __fs_dax_release(struct dax_device *dax_dev, void *owner)
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 02d6d042ee7f..8cc619fe347b 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -1,7 +1,6 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_MEMREMAP_H_
#define _LINUX_MEMREMAP_H_
-#include <linux/mm.h>
#include <linux/ioport.h>
#include <linux/percpu-refcount.h>

@@ -137,8 +136,6 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,

unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);
-
-static inline bool is_zone_device_page(const struct page *page);
#else
static inline void *devm_memremap_pages(struct device *dev,
struct dev_pagemap *pgmap)
@@ -169,20 +166,6 @@ static inline void vmem_altmap_free(struct vmem_altmap *altmap,
}
#endif /* CONFIG_ZONE_DEVICE */

-#if defined(CONFIG_DEVICE_PRIVATE) || defined(CONFIG_DEVICE_PUBLIC)
-static inline bool is_device_private_page(const struct page *page)
-{
- return is_zone_device_page(page) &&
- page->pgmap->type == MEMORY_DEVICE_PRIVATE;
-}
-
-static inline bool is_device_public_page(const struct page *page)
-{
- return is_zone_device_page(page) &&
- page->pgmap->type == MEMORY_DEVICE_PUBLIC;
-}
-#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
-
static inline void put_dev_pagemap(struct dev_pagemap *pgmap)
{
if (pgmap)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42adb1a..be9969e3cf09 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -812,27 +812,65 @@ static inline bool is_zone_device_page(const struct page *page)
}
#endif

-#if defined(CONFIG_DEVICE_PRIVATE) || defined(CONFIG_DEVICE_PUBLIC)
-void put_zone_device_private_or_public_page(struct page *page);
-DECLARE_STATIC_KEY_FALSE(device_private_key);
-#define IS_HMM_ENABLED static_branch_unlikely(&device_private_key)
-static inline bool is_device_private_page(const struct page *page);
-static inline bool is_device_public_page(const struct page *page);
-#else /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
-static inline void put_zone_device_private_or_public_page(struct page *page)
+#ifdef CONFIG_DEV_PAGEMAP_OPS
+void dev_pagemap_get_ops(void);
+void dev_pagemap_put_ops(void);
+void __put_devmap_managed_page(struct page *page);
+DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
+static inline bool put_devmap_managed_page(struct page *page)
+{
+ if (!static_branch_unlikely(&devmap_managed_key))
+ return false;
+ if (!is_zone_device_page(page))
+ return false;
+ switch (page->pgmap->type) {
+ case MEMORY_DEVICE_PRIVATE:
+ case MEMORY_DEVICE_PUBLIC:
+ case MEMORY_DEVICE_FS_DAX:
+ __put_devmap_managed_page(page);
+ return true;
+ default:
+ break;
+ }
+ return false;
+}
+
+static inline bool is_device_private_page(const struct page *page)
{
+ return is_zone_device_page(page) &&
+ page->pgmap->type == MEMORY_DEVICE_PRIVATE;
}
-#define IS_HMM_ENABLED 0
+
+static inline bool is_device_public_page(const struct page *page)
+{
+ return is_zone_device_page(page) &&
+ page->pgmap->type == MEMORY_DEVICE_PUBLIC;
+}
+
+#else /* CONFIG_DEV_PAGEMAP_OPS */
+static inline void dev_pagemap_get_ops(void)
+{
+}
+
+static inline void dev_pagemap_put_ops(void)
+{
+}
+
+static inline bool put_devmap_managed_page(struct page *page)
+{
+ return false;
+}
+
static inline bool is_device_private_page(const struct page *page)
{
return false;
}
+
static inline bool is_device_public_page(const struct page *page)
{
return false;
}
-#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
-
+#endif /* CONFIG_DEV_PAGEMAP_OPS */

static inline void get_page(struct page *page)
{
@@ -850,16 +888,13 @@ static inline void put_page(struct page *page)
page = compound_head(page);

/*
- * For private device pages we need to catch refcount transition from
- * 2 to 1, when refcount reach one it means the private device page is
- * free and we need to inform the device driver through callback. See
+ * For devmap managed pages we need to catch refcount transition from
+ * 2 to 1, when refcount reach one it means the page is free and we
+ * need to inform the device driver through callback. See
* include/linux/memremap.h and HMM for details.
*/
- if (IS_HMM_ENABLED && unlikely(is_device_private_page(page) ||
- unlikely(is_device_public_page(page)))) {
- put_zone_device_private_or_public_page(page);
+ if (put_devmap_managed_page(page))
return;
- }

if (put_page_testzero(page))
__put_page(page);
diff --git a/kernel/memremap.c b/kernel/memremap.c
index 52a2742f527f..07a6a405cf3d 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -302,8 +302,30 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
return pgmap;
}

-#if IS_ENABLED(CONFIG_DEVICE_PRIVATE) || IS_ENABLED(CONFIG_DEVICE_PUBLIC)
-void put_zone_device_private_or_public_page(struct page *page)
+#ifdef CONFIG_DEV_PAGEMAP_OPS
+DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
+EXPORT_SYMBOL_GPL(devmap_managed_key);
+static atomic_t devmap_enable;
+
+/*
+ * Toggle the static key for ->page_free() callbacks when dev_pagemap
+ * pages go idle.
+ */
+void dev_pagemap_get_ops(void)
+{
+ if (atomic_inc_return(&devmap_enable) == 1)
+ static_branch_enable(&devmap_managed_key);
+}
+EXPORT_SYMBOL_GPL(dev_pagemap_get_ops);
+
+void dev_pagemap_put_ops(void)
+{
+ if (atomic_dec_and_test(&devmap_enable))
+ static_branch_disable(&devmap_managed_key);
+}
+EXPORT_SYMBOL_GPL(dev_pagemap_put_ops);
+
+void __put_devmap_managed_page(struct page *page)
{
int count = page_ref_dec_return(page);

@@ -323,5 +345,5 @@ void put_zone_device_private_or_public_page(struct page *page)
} else if (!count)
__put_page(page);
}
-EXPORT_SYMBOL(put_zone_device_private_or_public_page);
-#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
+EXPORT_SYMBOL_GPL(__put_devmap_managed_page);
+#endif /* CONFIG_DEV_PAGEMAP_OPS */
diff --git a/mm/Kconfig b/mm/Kconfig
index c782e8fb7235..dc32828984a3 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -700,6 +700,9 @@ config ARCH_HAS_HMM
config MIGRATE_VMA_HELPER
bool

+config DEV_PAGEMAP_OPS
+ bool
+
config HMM
bool
select MIGRATE_VMA_HELPER
@@ -720,6 +723,7 @@ config DEVICE_PRIVATE
bool "Unaddressable device memory (GPU memory, ...)"
depends on ARCH_HAS_HMM
select HMM
+ select DEV_PAGEMAP_OPS

help
Allows creation of struct pages to represent unaddressable device
@@ -730,6 +734,7 @@ config DEVICE_PUBLIC
bool "Addressable device memory (like GPU memory)"
depends on ARCH_HAS_HMM
select HMM
+ select DEV_PAGEMAP_OPS

help
Allows creation of struct pages to represent addressable device
diff --git a/mm/hmm.c b/mm/hmm.c
index 320545b98ff5..4aa554e76d06 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -35,15 +35,6 @@

#define PA_SECTION_SIZE (1UL << PA_SECTION_SHIFT)

-#if defined(CONFIG_DEVICE_PRIVATE) || defined(CONFIG_DEVICE_PUBLIC)
-/*
- * Device private memory see HMM (Documentation/vm/hmm.txt) or hmm.h
- */
-DEFINE_STATIC_KEY_FALSE(device_private_key);
-EXPORT_SYMBOL(device_private_key);
-#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
-
-
#if IS_ENABLED(CONFIG_HMM_MIRROR)
static const struct mmu_notifier_ops hmm_mmu_notifier_ops;

@@ -996,7 +987,7 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
resource_size_t addr;
int ret;

- static_branch_enable(&device_private_key);
+ dev_pagemap_get_ops();

devmem = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
GFP_KERNEL, dev_to_node(device));
@@ -1090,7 +1081,7 @@ struct hmm_devmem *hmm_devmem_add_resource(const struct hmm_devmem_ops *ops,
if (res->desc != IORES_DESC_DEVICE_PUBLIC_MEMORY)
return ERR_PTR(-EINVAL);

- static_branch_enable(&device_private_key);
+ dev_pagemap_get_ops();

devmem = devres_alloc_node(&hmm_devmem_release, sizeof(*devmem),
GFP_KERNEL, dev_to_node(device));
diff --git a/mm/swap.c b/mm/swap.c
index 0f17330dd0e5..eed846cfc8b8 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -29,6 +29,7 @@
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/backing-dev.h>
+#include <linux/memremap.h>
#include <linux/memcontrol.h>
#include <linux/gfp.h>
#include <linux/uio.h>
@@ -744,7 +745,7 @@ void release_pages(struct page **pages, int nr)
flags);
locked_pgdat = NULL;
}
- put_zone_device_private_or_public_page(page);
+ put_devmap_managed_page(page);
continue;
}

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