Re: [PATCH v7 08/14] mm, dax: enable filesystems to trigger dev_pagemap ->page_free callbacks

Jan Kara
2018-03-29T16:36:56Z

On Wed 21-03-18 15:57:53, Dan Williams wrote:
> In order to resolve collisions between filesystem operations and DMA to
> DAX mapped pages we need a callback when DMA completes. With a callback
> we can hold off filesystem operations while DMA is in-flight and then
> resume those operations when the last put_page() occurs on a DMA page.
>
> Recall that the 'struct page' entries for DAX memory are created with
> devm_memremap_pages(). That routine arranges for the pages to be
> allocated, but never onlined, so a DAX page is DMA-idle when its
> reference count reaches one.
>
> Also recall that the HMM sub-system added infrastructure to trap the
> page-idle (2-to-1 reference count) transition of the pages allocated by
> devm_memremap_pages() and trigger a callback via the 'struct
> dev_pagemap' associated with the page range. Whereas the HMM callbacks
> are going to a device driver to manage bounce pages in device-memory in
> the filesystem-dax case we will call back to filesystem specified
> callback.
>
> Since the callback is not known at devm_memremap_pages() time we arrange
> for the filesystem to install it at mount time. No functional changes
> are expected as this only registers a nop handler for the ->page_free()
> event for device-mapped pages.
>
> Cc: Michal Hocko <mhocko@suse.com>
> Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

The patch looks good to me. You can add:

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

Honza

> ---
> drivers/dax/super.c | 79 ++++++++++++++++++++++++++++++++++++++++------
> drivers/nvdimm/pmem.c | 3 +-
> fs/ext2/super.c | 6 ++-
> fs/ext4/super.c | 6 ++-
> fs/xfs/xfs_super.c | 20 ++++++------
> include/linux/dax.h | 17 +++++-----
> include/linux/memremap.h | 8 +++++
> 7 files changed, 103 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 2b2332b605e4..ecefe9f7eb60 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -29,6 +29,7 @@ static struct vfsmount *dax_mnt;
> static DEFINE_IDA(dax_minor_ida);
> static struct kmem_cache *dax_cache __read_mostly;
> static struct super_block *dax_superblock __read_mostly;
> +static DEFINE_MUTEX(devmap_lock);
>
> #define DAX_HASH_SIZE (PAGE_SIZE / sizeof(struct hlist_head))
> static struct hlist_head dax_host_list[DAX_HASH_SIZE];
> @@ -62,16 +63,6 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
> }
> EXPORT_SYMBOL(bdev_dax_pgoff);
>
> -#if IS_ENABLED(CONFIG_FS_DAX)
> -struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> -{
> - if (!blk_queue_dax(bdev->bd_queue))
> - return NULL;
> - return fs_dax_get_by_host(bdev->bd_disk->disk_name);
> -}
> -EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
> -#endif
> -
> /**
> * __bdev_dax_supported() - Check if the device supports dax for filesystem
> * @sb: The superblock of the device
> @@ -169,9 +160,66 @@ struct dax_device {
> const char *host;
> void *private;
> unsigned long flags;
> + struct dev_pagemap *pgmap;
> const struct dax_operations *ops;
> };
>
> +#if IS_ENABLED(CONFIG_FS_DAX)
> +static void generic_dax_pagefree(struct page *page, void *data)
> +{
> + /* TODO: wakeup page-idle waiters */
> +}
> +
> +struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner)
> +{
> + struct dax_device *dax_dev;
> + struct dev_pagemap *pgmap;
> +
> + if (!blk_queue_dax(bdev->bd_queue))
> + return NULL;
> + dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
> + if (!dax_dev->pgmap)
> + return dax_dev;
> + pgmap = dax_dev->pgmap;
> +
> + mutex_lock(&devmap_lock);
> + if ((pgmap->data && pgmap->data != owner) || pgmap->page_free
> + || pgmap->page_fault
> + || pgmap->type != MEMORY_DEVICE_HOST) {
> + put_dax(dax_dev);
> + mutex_unlock(&devmap_lock);
> + return NULL;
> + }
> +
> + pgmap->type = MEMORY_DEVICE_FS_DAX;
> + pgmap->page_free = generic_dax_pagefree;
> + pgmap->data = owner;
> + mutex_unlock(&devmap_lock);
> +
> + return dax_dev;
> +}
> +EXPORT_SYMBOL_GPL(fs_dax_claim_bdev);
> +
> +void fs_dax_release(struct dax_device *dax_dev, void *owner)
> +{
> + struct dev_pagemap *pgmap = dax_dev ? dax_dev->pgmap : NULL;
> +
> + put_dax(dax_dev);
> + if (!pgmap)
> + return;
> + if (!pgmap->data)
> + return;
> +
> + mutex_lock(&devmap_lock);
> + WARN_ON(pgmap->data != owner);
> + pgmap->type = MEMORY_DEVICE_HOST;
> + pgmap->page_free = NULL;
> + pgmap->data = NULL;
> + mutex_unlock(&devmap_lock);
> +}
> +EXPORT_SYMBOL_GPL(fs_dax_release);
> +#endif
> +
> static ssize_t write_cache_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> @@ -499,6 +547,17 @@ struct dax_device *alloc_dax(void *private, const char *__host,
> }
> EXPORT_SYMBOL_GPL(alloc_dax);
>
> +struct dax_device *alloc_dax_devmap(void *private, const char *host,
> + const struct dax_operations *ops, struct dev_pagemap *pgmap)
> +{
> + struct dax_device *dax_dev = alloc_dax(private, host, ops);
> +
> + if (dax_dev)
> + dax_dev->pgmap = pgmap;
> + return dax_dev;
> +}
> +EXPORT_SYMBOL_GPL(alloc_dax_devmap);
> +
> void put_dax(struct dax_device *dax_dev)
> {
> if (!dax_dev)
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 06f8dcc52ca6..e6d7351f3379 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -408,7 +408,8 @@ static int pmem_attach_disk(struct device *dev,
> nvdimm_badblocks_populate(nd_region, &pmem->bb, &bb_res);
> disk->bb = &pmem->bb;
>
> - dax_dev = alloc_dax(pmem, disk->disk_name, &pmem_dax_ops);
> + dax_dev = alloc_dax_devmap(pmem, disk->disk_name, &pmem_dax_ops,
> + &pmem->pgmap);
> if (!dax_dev) {
> put_disk(disk);
> return -ENOMEM;
> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 7666c065b96f..6ae20e319bc4 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -172,7 +172,7 @@ static void ext2_put_super (struct super_block * sb)
> brelse (sbi->s_sbh);
> sb->s_fs_info = NULL;
> kfree(sbi->s_blockgroup_lock);
> - fs_put_dax(sbi->s_daxdev);
> + fs_dax_release(sbi->s_daxdev, sb);
> kfree(sbi);
> }
>
> @@ -817,7 +817,7 @@ static unsigned long descriptor_loc(struct super_block *sb,
>
> static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> {
> - struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
> + struct dax_device *dax_dev = fs_dax_claim_bdev(sb->s_bdev, sb);
> struct buffer_head * bh;
> struct ext2_sb_info * sbi;
> struct ext2_super_block * es;
> @@ -1213,7 +1213,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> kfree(sbi->s_blockgroup_lock);
> kfree(sbi);
> failed:
> - fs_put_dax(dax_dev);
> + fs_dax_release(dax_dev, sb);
> return ret;
> }
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 39bf464c35f1..315a323729e3 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -952,7 +952,7 @@ static void ext4_put_super(struct super_block *sb)
> if (sbi->s_chksum_driver)
> crypto_free_shash(sbi->s_chksum_driver);
> kfree(sbi->s_blockgroup_lock);
> - fs_put_dax(sbi->s_daxdev);
> + fs_dax_release(sbi->s_daxdev, sb);
> kfree(sbi);
> }
>
> @@ -3398,7 +3398,7 @@ static void ext4_set_resv_clusters(struct super_block *sb)
>
> static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> {
> - struct dax_device *dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
> + struct dax_device *dax_dev = fs_dax_claim_bdev(sb->s_bdev, sb);
> char *orig_data = kstrdup(data, GFP_KERNEL);
> struct buffer_head *bh;
> struct ext4_super_block *es = NULL;
> @@ -4408,7 +4408,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> out_free_base:
> kfree(sbi);
> kfree(orig_data);
> - fs_put_dax(dax_dev);
> + fs_dax_release(dax_dev, sb);
> return err ? err : ret;
> }
>
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 93588ea3d3d2..ef7dd7148c0b 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -724,7 +724,7 @@ xfs_close_devices(
>
> xfs_free_buftarg(mp, mp->m_logdev_targp);
> xfs_blkdev_put(logdev);
> - fs_put_dax(dax_logdev);
> + fs_dax_release(dax_logdev, mp);
> }
> if (mp->m_rtdev_targp) {
> struct block_device *rtdev = mp->m_rtdev_targp->bt_bdev;
> @@ -732,10 +732,10 @@ xfs_close_devices(
>
> xfs_free_buftarg(mp, mp->m_rtdev_targp);
> xfs_blkdev_put(rtdev);
> - fs_put_dax(dax_rtdev);
> + fs_dax_release(dax_rtdev, mp);
> }
> xfs_free_buftarg(mp, mp->m_ddev_targp);
> - fs_put_dax(dax_ddev);
> + fs_dax_release(dax_ddev, mp);
> }
>
> /*
> @@ -753,9 +753,9 @@ xfs_open_devices(
> struct xfs_mount *mp)
> {
> struct block_device *ddev = mp->m_super->s_bdev;
> - struct dax_device *dax_ddev = fs_dax_get_by_bdev(ddev);
> - struct dax_device *dax_logdev = NULL, *dax_rtdev = NULL;
> + struct dax_device *dax_ddev = fs_dax_claim_bdev(ddev, mp);
> struct block_device *logdev = NULL, *rtdev = NULL;
> + struct dax_device *dax_logdev = NULL, *dax_rtdev = NULL;
> int error;
>
> /*
> @@ -765,7 +765,7 @@ xfs_open_devices(
> error = xfs_blkdev_get(mp, mp->m_logname, &logdev);
> if (error)
> goto out;
> - dax_logdev = fs_dax_get_by_bdev(logdev);
> + dax_logdev = fs_dax_claim_bdev(logdev, mp);
> }
>
> if (mp->m_rtname) {
> @@ -779,7 +779,7 @@ xfs_open_devices(
> error = -EINVAL;
> goto out_close_rtdev;
> }
> - dax_rtdev = fs_dax_get_by_bdev(rtdev);
> + dax_rtdev = fs_dax_claim_bdev(rtdev, mp);
> }
>
> /*
> @@ -813,14 +813,14 @@ xfs_open_devices(
> xfs_free_buftarg(mp, mp->m_ddev_targp);
> out_close_rtdev:
> xfs_blkdev_put(rtdev);
> - fs_put_dax(dax_rtdev);
> + fs_dax_release(dax_rtdev, mp);
> out_close_logdev:
> if (logdev && logdev != ddev) {
> xfs_blkdev_put(logdev);
> - fs_put_dax(dax_logdev);
> + fs_dax_release(dax_logdev, mp);
> }
> out:
> - fs_put_dax(dax_ddev);
> + fs_dax_release(dax_ddev, mp);
> return error;
> }
>
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index ae27a7efe7ab..92a1d3ee1615 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -52,12 +52,8 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
> return dax_get_by_host(host);
> }
>
> -static inline void fs_put_dax(struct dax_device *dax_dev)
> -{
> - put_dax(dax_dev);
> -}
> -
> -struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
> +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);
> #else
> @@ -71,13 +67,14 @@ static inline struct dax_device *fs_dax_get_by_host(const char *host)
> return NULL;
> }
>
> -static inline void fs_put_dax(struct dax_device *dax_dev)
> +static inline struct dax_device *fs_dax_claim_bdev(struct block_device *bdev,
> + void *owner)
> {
> + return NULL;
> }
>
> -static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> +static inline void fs_dax_release(struct dax_device *dax_dev, void *owner)
> {
> - return NULL;
> }
>
> static inline int dax_writeback_mapping_range(struct address_space *mapping,
> @@ -91,6 +88,8 @@ int dax_read_lock(void);
> void dax_read_unlock(int id);
> struct dax_device *alloc_dax(void *private, const char *host,
> const struct dax_operations *ops);
> +struct dax_device *alloc_dax_devmap(void *private, const char *host,
> + const struct dax_operations *ops, struct dev_pagemap *pgmap);
> bool dax_alive(struct dax_device *dax_dev);
> void kill_dax(struct dax_device *dax_dev);
> void *dax_get_private(struct dax_device *dax_dev);
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 7b4899c06f49..02d6d042ee7f 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -53,11 +53,19 @@ struct vmem_altmap {
> * driver can hotplug the device memory using ZONE_DEVICE and with that memory
> * type. Any page of a process can be migrated to such memory. However no one
> * should be allow to pin such memory so that it can always be evicted.
> + *
> + * MEMORY_DEVICE_FS_DAX:
> + * When MEMORY_DEVICE_HOST memory is represented by a device that can
> + * host a filesystem, for example /dev/pmem0, that filesystem can
> + * register for a callback when a page is idled. For the filesystem-dax
> + * case page idle callbacks are used to coordinate DMA vs
> + * hole-punch/truncate.
> */
> enum memory_type {
> MEMORY_DEVICE_HOST = 0,
> MEMORY_DEVICE_PRIVATE,
> MEMORY_DEVICE_PUBLIC,
> + MEMORY_DEVICE_FS_DAX,
> };
>
> /*
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR