Re: [PATCH v7 09/14] mm, dev_pagemap: introduce CONFIG_DEV_PAGEMAP_OPS

Jan Kara
2018-03-30T10:37:56Z

On Wed 21-03-18 15:57:59, Dan Williams wrote:
> 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.
>
> Cc: Michal Hocko <mhocko@suse.com>
> Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> drivers/dax/super.c | 2 ++
> fs/Kconfig | 1 +
> include/linux/memremap.h | 20 ++-------------
> include/linux/mm.h | 61 ++++++++++++++++++++++++++++++++--------------
> kernel/memremap.c | 30 ++++++++++++++++++++---
> mm/Kconfig | 5 ++++
> mm/hmm.c | 13 ++--------
> mm/swap.c | 3 ++
> 8 files changed, 84 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index ecefe9f7eb60..619b1ed6434c 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -191,6 +191,7 @@ struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner)
> return NULL;
> }
>
> + dev_pagemap_get_ops();
> pgmap->type = MEMORY_DEVICE_FS_DAX;
> pgmap->page_free = generic_dax_pagefree;
> pgmap->data = owner;
> @@ -215,6 +216,7 @@ 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..1f0832bbc32f 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
> select FS_IOMAP
> select DAX
> help
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 02d6d042ee7f..9faf25d6abef 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>
>
> @@ -130,6 +129,9 @@ struct dev_pagemap {
> enum memory_type type;
> };
>
> +void dev_pagemap_get_ops(void);
> +void dev_pagemap_put_ops(void);
> +
> #ifdef CONFIG_ZONE_DEVICE
> void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap);
> struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> @@ -137,8 +139,6 @@ 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 +169,6 @@ 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..088c76bce360 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -812,27 +812,55 @@ 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 __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;
> }
> -#define IS_HMM_ENABLED 0
> +
> static inline bool is_device_private_page(const struct page *page)
> {
> - return false;
> + 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;
> +}
> +
> +#else /* CONFIG_DEV_PAGEMAP_OPS */
> +static inline bool put_devmap_managed_page(struct page *page)
> +{
> return false;
> }
> -#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
>
> +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_DEV_PAGEMAP_OPS */
>
> static inline void get_page(struct page *page)
> {
> @@ -850,16 +878,13 @@ 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 4dd4274cabe2..72d0bb6fc47d 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -476,8 +476,30 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> }
> #endif /* CONFIG_ZONE_DEVICE */
>
> -#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);
>
> @@ -497,5 +519,5 @@ 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;
> }
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR