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SubjectRe: [PATCH v8 10/18] dax, dm: introduce ->fs_{claim, release}() dax_device infrastructure
On Fri, Mar 30, 2018 at 9:03 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> In preparation for allowing filesystems to augment the dev_pagemap
> associated with a dax_device, add an ->fs_claim() callback. The
> ->fs_claim() callback is leveraged by the device-mapper dax
> implementation to iterate all member devices in the map and repeat the
> claim operation across the array.
>
> 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.
> The ->fs_claim() operation arranges for this callback to be registered,
> although that implementation is saved for a later patch.
>
> Cc: Alasdair Kergon <agk@redhat.com>
> Cc: Mike Snitzer <snitzer@redhat.com>

Mike, do these DM touches look ok to you? We need these ->fs_claim()
/ ->fs_release() interfaces for device-mapper to set up filesystem-dax
infrastructure on all sub-devices whenever a dax-capable DM device is
mounted. It builds on the device-mapper dax dependency removal
patches.

> Cc: Matthew Wilcox <mawilcox@microsoft.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Jan Kara <jack@suse.cz>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> drivers/dax/super.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++
> drivers/md/dm.c | 56 ++++++++++++++++++++++++++++++++
> include/linux/dax.h | 16 +++++++++
> include/linux/memremap.h | 8 +++++
> 4 files changed, 160 insertions(+)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 2b2332b605e4..c4cf284dfe1c 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];
> @@ -169,9 +170,88 @@ 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(struct dax_device *dax_dev, void *owner)
> +{
> + struct dev_pagemap *pgmap;
> +
> + if (!dax_dev->pgmap)
> + return dax_dev;
> + pgmap = dax_dev->pgmap;
> +
> + mutex_lock(&devmap_lock);
> + if (pgmap->data && pgmap->data == owner) {
> + /* dm might try to claim the same device more than once... */
> + mutex_unlock(&devmap_lock);
> + return dax_dev;
> + } else if (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);
> +
> +struct dax_device *fs_dax_claim_bdev(struct block_device *bdev, void *owner)
> +{
> + struct dax_device *dax_dev;
> +
> + if (!blk_queue_dax(bdev->bd_queue))
> + return NULL;
> + dax_dev = fs_dax_get_by_host(bdev->bd_disk->disk_name);
> + if (dax_dev->ops->fs_claim)
> + return dax_dev->ops->fs_claim(dax_dev, owner);
> + else
> + return fs_dax_claim(dax_dev, owner);
> +}
> +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);
> +
> +void fs_dax_release(struct dax_device *dax_dev, void *owner)
> +{
> + if (dax_dev->ops->fs_release)
> + dax_dev->ops->fs_release(dax_dev, owner);
> + else
> + __fs_dax_release(dax_dev, owner);
> +}
> +EXPORT_SYMBOL_GPL(fs_dax_release);
> +#endif
> +
> static ssize_t write_cache_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index ffc93aecc02a..964cb7537f11 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1090,6 +1090,60 @@ static size_t dm_dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
> return ret;
> }
>
> +static int dm_dax_dev_claim(struct dm_target *ti, struct dm_dev *dev,
> + sector_t start, sector_t len, void *owner)
> +{
> + if (fs_dax_claim(dev->dax_dev, owner))
> + return 0;
> + /*
> + * Outside of a kernel bug there is no reason a dax_dev should
> + * fail a claim attempt. Device-mapper should have exclusive
> + * ownership of the dm_dev and the filesystem should have
> + * exclusive ownership of the dm_target.
> + */
> + WARN_ON_ONCE(1);
> + return -ENXIO;
> +}
> +
> +static int dm_dax_dev_release(struct dm_target *ti, struct dm_dev *dev,
> + sector_t start, sector_t len, void *owner)
> +{
> + __fs_dax_release(dev->dax_dev, owner);
> + return 0;
> +}
> +
> +static struct dax_device *dm_dax_iterate(struct dax_device *dax_dev,
> + iterate_devices_callout_fn fn, void *arg)
> +{
> + struct mapped_device *md = dax_get_private(dax_dev);
> + struct dm_table *map;
> + struct dm_target *ti;
> + int i, srcu_idx;
> +
> + map = dm_get_live_table(md, &srcu_idx);
> +
> + for (i = 0; i < dm_table_get_num_targets(map); i++) {
> + ti = dm_table_get_target(map, i);
> +
> + if (ti->type->iterate_devices)
> + ti->type->iterate_devices(ti, fn, arg);
> + }
> +
> + dm_put_live_table(md, srcu_idx);
> + return dax_dev;
> +}
> +
> +static struct dax_device *dm_dax_fs_claim(struct dax_device *dax_dev,
> + void *owner)
> +{
> + return dm_dax_iterate(dax_dev, dm_dax_dev_claim, owner);
> +}
> +
> +static void dm_dax_fs_release(struct dax_device *dax_dev, void *owner)
> +{
> + dm_dax_iterate(dax_dev, dm_dax_dev_release, owner);
> +}
> +
> /*
> * A target may call dm_accept_partial_bio only from the map routine. It is
> * allowed for all bio types except REQ_PREFLUSH and REQ_OP_ZONE_RESET.
> @@ -3111,6 +3165,8 @@ static const struct block_device_operations dm_blk_dops = {
> static const struct dax_operations dm_dax_ops = {
> .direct_access = dm_dax_direct_access,
> .copy_from_iter = dm_dax_copy_from_iter,
> + .fs_claim = dm_dax_fs_claim,
> + .fs_release = dm_dax_fs_release,
> };
>
> /*
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index f9eb22ad341e..e9d59a6b06e1 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -20,6 +20,10 @@ struct dax_operations {
> /* copy_from_iter: required operation for fs-dax direct-i/o */
> size_t (*copy_from_iter)(struct dax_device *, pgoff_t, void *, size_t,
> struct iov_iter *);
> + /* fs_claim: setup filesytem parameters for the device's dev_pagemap */
> + struct dax_device *(*fs_claim)(struct dax_device *, void *);
> + /* fs_release: restore device's dev_pagemap to its default state */
> + void (*fs_release)(struct dax_device *, void *);
> };
>
> extern struct attribute_group dax_attribute_group;
> @@ -83,6 +87,8 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
> struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
> 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)
> {
> @@ -108,6 +114,16 @@ static inline int dax_writeback_mapping_range(struct address_space *mapping,
> {
> return -EOPNOTSUPP;
> }
> +
> +static inline struct dax_device *fs_dax_claim(struct dax_device *dax_dev,
> + void *owner)
> +{
> + return NULL;
> +}
> +
> +static inline void __fs_dax_release(struct dax_device *dax_dev, void *owner)
> +{
> +}
> #endif
>
> int dax_read_lock(void);
> 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,
> };
>
> /*
>

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