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Commit e7638488 authored by Dan Williams's avatar Dan Williams
Browse files

mm: introduce MEMORY_DEVICE_FS_DAX and CONFIG_DEV_PAGEMAP_OPS 



In preparation for fixing dax-dma-vs-unmap issues, filesystems need to
be able to rely on the fact that they will get wakeups on dev_pagemap
page-idle events. Introduce MEMORY_DEVICE_FS_DAX and
generic_dax_page_free() as common indicator / infrastructure for dax
filesytems to require. With this change there are no users of the
MEMORY_DEVICE_HOST designation, so remove it.

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: default avatarkbuild test robot <lkp@intel.com>
Reported-by: default avatarThomas Meyer <thomas@m3y3r.de>
Reported-by: default avatarDave Jiang <dave.jiang@intel.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 5981690d

drivers/dax/super.c

+11 −3
Original line number Diff line number Diff line
@@ -86,6 +86,7 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize) 
{

	struct block_device *bdev = sb->s_bdev;

	struct dax_device *dax_dev;

	bool dax_enabled = false;

	pgoff_t pgoff;

	int err, id;

	void *kaddr;
@@ -134,14 +135,21 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize) 
		 * on being able to do (page_address(pfn_to_page())).

		 */

		WARN_ON(IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API));

		dax_enabled = true;

	} else if (pfn_t_devmap(pfn)) {

		/* pass */;

	} else {

		struct dev_pagemap *pgmap;



		pgmap = get_dev_pagemap(pfn_t_to_pfn(pfn), NULL);

		if (pgmap && pgmap->type == MEMORY_DEVICE_FS_DAX)

			dax_enabled = true;

		put_dev_pagemap(pgmap);

	}



	if (!dax_enabled) {

		pr_debug("VFS (%s): error: dax support not enabled\n",

				sb->s_id);

		return -EOPNOTSUPP;

	}



	return 0;

}

EXPORT_SYMBOL_GPL(__bdev_dax_supported);

drivers/nvdimm/pfn_devs.c

+0 −2
Original line number Diff line number Diff line
@@ -561,8 +561,6 @@ static int __nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap) 
	res->start += start_pad;

	res->end -= end_trunc;



	pgmap->type = MEMORY_DEVICE_HOST;



	if (nd_pfn->mode == PFN_MODE_RAM) {

		if (offset < SZ_8K)

			return -EINVAL;

drivers/nvdimm/pmem.c

+25 −0
Original line number Diff line number Diff line
@@ -294,6 +294,27 @@ static void pmem_release_disk(void *__pmem) 
	put_disk(pmem->disk);

}



static void pmem_release_pgmap_ops(void *__pgmap)

{

	dev_pagemap_put_ops();

}



static void fsdax_pagefree(struct page *page, void *data)

{

	wake_up_var(&page->_refcount);

}



static int setup_pagemap_fsdax(struct device *dev, struct dev_pagemap *pgmap)

{

	dev_pagemap_get_ops();

	if (devm_add_action_or_reset(dev, pmem_release_pgmap_ops, pgmap))

		return -ENOMEM;

	pgmap->type = MEMORY_DEVICE_FS_DAX;

	pgmap->page_free = fsdax_pagefree;



	return 0;

}



static int pmem_attach_disk(struct device *dev,

		struct nd_namespace_common *ndns)

{
@@ -353,6 +374,8 @@ static int pmem_attach_disk(struct device *dev, 
	pmem->pfn_flags = PFN_DEV;

	pmem->pgmap.ref = &q->q_usage_counter;

	if (is_nd_pfn(dev)) {

		if (setup_pagemap_fsdax(dev, &pmem->pgmap))

			return -ENOMEM;

		addr = devm_memremap_pages(dev, &pmem->pgmap);

		pfn_sb = nd_pfn->pfn_sb;

		pmem->data_offset = le64_to_cpu(pfn_sb->dataoff);
@@ -364,6 +387,8 @@ static int pmem_attach_disk(struct device *dev, 
	} else if (pmem_should_map_pages(dev)) {

		memcpy(&pmem->pgmap.res, &nsio->res, sizeof(pmem->pgmap.res));

		pmem->pgmap.altmap_valid = false;

		if (setup_pagemap_fsdax(dev, &pmem->pgmap))

			return -ENOMEM;

		addr = devm_memremap_pages(dev, &pmem->pgmap);

		pmem->pfn_flags |= PFN_MAP;

		memcpy(&bb_res, &pmem->pgmap.res, sizeof(bb_res));

fs/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

include/linux/memremap.h

+10 −26
Original line number Diff line number Diff line 
/* 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>
@@ -30,13 +29,6 @@ struct vmem_altmap { 
 * Specialize ZONE_DEVICE memory into multiple types each having differents

 * usage.

 *

 * MEMORY_DEVICE_HOST:

 * Persistent device memory (pmem): struct page might be allocated in different

 * memory and architecture might want to perform special actions. It is similar

 * to regular memory, in that the CPU can access it transparently. However,

 * it is likely to have different bandwidth and latency than regular memory.

 * See Documentation/nvdimm/nvdimm.txt for more information.

 *

 * MEMORY_DEVICE_PRIVATE:

 * Device memory that is not directly addressable by the CPU: CPU can neither

 * read nor write private memory. In this case, we do still have struct pages
@@ -53,11 +45,19 @@ 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:

 * Host memory that has similar access semantics as System RAM i.e. DMA

 * coherent and supports page pinning. In support of coordinating page

 * pinning vs other operations MEMORY_DEVICE_FS_DAX arranges for a

 * wakeup event whenever a page is unpinned and becomes idle. This

 * wakeup is used to coordinate physical address space management (ex:

 * fs truncate/hole punch) vs pinned pages (ex: device dma).

 */

enum memory_type {

	MEMORY_DEVICE_HOST = 0,

	MEMORY_DEVICE_PRIVATE,

	MEMORY_DEVICE_PRIVATE = 1,

	MEMORY_DEVICE_PUBLIC,

	MEMORY_DEVICE_FS_DAX,

};



/*
@@ -129,8 +129,6 @@ 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)
@@ -161,20 +159,6 @@ 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)