Commit 5212e11f authored by Vishal Verma's avatar Vishal Verma Committed by Dan Williams

nd_btt: atomic sector updates

BTT stands for Block Translation Table, and is a way to provide power
fail sector atomicity semantics for block devices that have the ability
to perform byte granularity IO. It relies on the capability of libnvdimm
namespace devices to do byte aligned IO.

The BTT works as a stacked blocked device, and reserves a chunk of space
from the backing device for its accounting metadata. It is a bio-based
driver because all IO is done synchronously, and there is no queuing or
asynchronous completions at either the device or the driver level.

The BTT uses 'lanes' to index into various 'on-disk' data structures,
and lanes also act as a synchronization mechanism in case there are more
CPUs than available lanes. We did a comparison between two lane lock
strategies - first where we kept an atomic counter around that tracked
which was the last lane that was used, and 'our' lane was determined by
atomically incrementing that. That way, for the nr_cpus > nr_lanes case,
theoretically, no CPU would be blocked waiting for a lane. The other
strategy was to use the cpu number we're scheduled on to and hash it to
a lane number. Theoretically, this could block an IO that could've
otherwise run using a different, free lane. But some fio workloads
showed that the direct cpu -> lane hash performed faster than tracking
'last lane' - my reasoning is the cache thrash caused by moving the
atomic variable made that approach slower than simply waiting out the
in-progress IO. This supports the conclusion that the driver can be a
very simple bio-based one that does synchronous IOs instead of queuing.

Cc: Andy Lutomirski <>
Cc: Boaz Harrosh <>
Cc: H. Peter Anvin <>
Cc: Jens Axboe <>
Cc: Ingo Molnar <>
Cc: Christoph Hellwig <>
Cc: Neil Brown <>
Cc: Jeff Moyer <>
Cc: Dave Chinner <>
Cc: Greg KH <>
[jmoyer: fix nmi watchdog timeout in btt_map_init]
[jmoyer: move btt initialization to module load path]
[jmoyer: fix memory leak in the btt initialization path]
[jmoyer: Don't overwrite corrupted arenas]
Signed-off-by: default avatarVishal Verma <>
Signed-off-by: default avatarDan Williams <>
parent 8c2f7e86
This diff is collapsed.
......@@ -902,6 +902,7 @@ static int acpi_nfit_init_mapping(struct acpi_nfit_desc *acpi_desc,
} else {
nd_mapping->size = nfit_mem->bdw->capacity;
nd_mapping->start = nfit_mem->bdw->start_address;
ndr_desc->num_lanes = nfit_mem->bdw->windows;
blk_valid = 1;
......@@ -8,11 +8,11 @@ menuconfig LIBNVDIMM
NFIT, or otherwise can discover NVDIMM resources, a libnvdimm
bus is registered to advertise PMEM (persistent memory)
namespaces (/dev/pmemX) and BLK (sliding mmio window(s))
namespaces (/dev/ndX). A PMEM namespace refers to a memory
resource that may span multiple DIMMs and support DAX (see
CONFIG_DAX). A BLK namespace refers to an NVDIMM control
region which exposes an mmio register set for windowed
access mode to non-volatile memory.
namespaces (/dev/ndblkX.Y). A PMEM namespace refers to a
memory resource that may span multiple DIMMs and support DAX
(see CONFIG_DAX). A BLK namespace refers to an NVDIMM control
region which exposes an mmio register set for windowed access
mode to non-volatile memory.
......@@ -20,6 +20,7 @@ config BLK_DEV_PMEM
tristate "PMEM: Persistent memory block device support"
depends on HAS_IOMEM
select ND_BTT if BTT
Memory ranges for PMEM are described by either an NFIT
(NVDIMM Firmware Interface Table, see CONFIG_NFIT_ACPI), a
......@@ -33,7 +34,22 @@ config BLK_DEV_PMEM
Say Y if you want to use an NVDIMM
config ND_BTT
config BTT
def_bool y
bool "BTT: Block Translation Table (atomic sector updates)"
default y if LIBNVDIMM
The Block Translation Table (BTT) provides atomic sector
update semantics for persistent memory devices, so that
applications that rely on sector writes not being torn (a
guarantee that typical disks provide) can continue to do so.
The BTT manifests itself as an alternate personality for an
NVDIMM namespace, i.e. a namespace can be in raw mode (pmemX,
ndblkX.Y, etc...), or 'sectored' mode, (pmemXs, ndblkX.Ys,
Select Y if unsure
obj-$(CONFIG_LIBNVDIMM) += libnvdimm.o
obj-$(CONFIG_BLK_DEV_PMEM) += nd_pmem.o
obj-$(CONFIG_ND_BTT) += nd_btt.o
nd_pmem-y := pmem.o
nd_btt-y := btt.o
libnvdimm-y := core.o
libnvdimm-y += bus.o
libnvdimm-y += dimm_devs.o
This diff is collapsed.
......@@ -19,6 +19,39 @@
#define BTT_SIG_LEN 16
#define MAP_ENT_SIZE 4
#define MAP_TRIM_SHIFT 31
#define MAP_ERR_SHIFT 30
#define MAP_LBA_MASK (~((1 << MAP_TRIM_SHIFT) | (1 << MAP_ERR_SHIFT)))
#define MAP_ENT_NORMAL 0xC0000000
#define LOG_ENT_SIZE sizeof(struct log_entry)
#define ARENA_MIN_SIZE (1UL << 24) /* 16 MB */
#define ARENA_MAX_SIZE (1ULL << 39) /* 512 GB */
#define RTT_VALID (1UL << 31)
#define RTT_INVALID 0
#define BTT_PG_SIZE 4096
#define LOG_SEQ_INIT 1
#define IB_FLAG_ERROR 0x00000001
#define IB_FLAG_ERROR_MASK 0x00000001
enum btt_init_state {
struct log_entry {
__le32 lba;
__le32 old_map;
__le32 new_map;
__le32 seq;
__le64 padding[2];
struct btt_sb {
u8 signature[BTT_SIG_LEN];
......@@ -42,4 +75,112 @@ struct btt_sb {
__le64 checksum;
struct free_entry {
u32 block;
u8 sub;
u8 seq;
struct aligned_lock {
union {
spinlock_t lock;
u8 cacheline_padding[L1_CACHE_BYTES];
* struct arena_info - handle for an arena
* @size: Size in bytes this arena occupies on the raw device.
* This includes arena metadata.
* @external_lba_start: The first external LBA in this arena.
* @internal_nlba: Number of internal blocks available in the arena
* including nfree reserved blocks
* @internal_lbasize: Internal and external lba sizes may be different as
* we can round up 'odd' external lbasizes such as 520B
* to be aligned.
* @external_nlba: Number of blocks contributed by the arena to the number
* reported to upper layers. (internal_nlba - nfree)
* @external_lbasize: LBA size as exposed to upper layers.
* @nfree: A reserve number of 'free' blocks that is used to
* handle incoming writes.
* @version_major: Metadata layout version major.
* @version_minor: Metadata layout version minor.
* @nextoff: Offset in bytes to the start of the next arena.
* @infooff: Offset in bytes to the info block of this arena.
* @dataoff: Offset in bytes to the data area of this arena.
* @mapoff: Offset in bytes to the map area of this arena.
* @logoff: Offset in bytes to the log area of this arena.
* @info2off: Offset in bytes to the backup info block of this arena.
* @freelist: Pointer to in-memory list of free blocks
* @rtt: Pointer to in-memory "Read Tracking Table"
* @map_locks: Spinlocks protecting concurrent map writes
* @nd_btt: Pointer to parent nd_btt structure.
* @list: List head for list of arenas
* @debugfs_dir: Debugfs dentry
* @flags: Arena flags - may signify error states.
* arena_info is a per-arena handle. Once an arena is narrowed down for an
* IO, this struct is passed around for the duration of the IO.
struct arena_info {
u64 size; /* Total bytes for this arena */
u64 external_lba_start;
u32 internal_nlba;
u32 internal_lbasize;
u32 external_nlba;
u32 external_lbasize;
u32 nfree;
u16 version_major;
u16 version_minor;
/* Byte offsets to the different on-media structures */
u64 nextoff;
u64 infooff;
u64 dataoff;
u64 mapoff;
u64 logoff;
u64 info2off;
/* Pointers to other in-memory structures for this arena */
struct free_entry *freelist;
u32 *rtt;
struct aligned_lock *map_locks;
struct nd_btt *nd_btt;
struct list_head list;
struct dentry *debugfs_dir;
/* Arena flags */
u32 flags;
* struct btt - handle for a BTT instance
* @btt_disk: Pointer to the gendisk for BTT device
* @btt_queue: Pointer to the request queue for the BTT device
* @arena_list: Head of the list of arenas
* @debugfs_dir: Debugfs dentry
* @nd_btt: Parent nd_btt struct
* @nlba: Number of logical blocks exposed to the upper layers
* after removing the amount of space needed by metadata
* @rawsize: Total size in bytes of the available backing device
* @lbasize: LBA size as requested and presented to upper layers.
* This is sector_size + size of any metadata.
* @sector_size: The Linux sector size - 512 or 4096
* @lanes: Per-lane spinlocks
* @init_lock: Mutex used for the BTT initialization
* @init_state: Flag describing the initialization state for the BTT
* @num_arenas: Number of arenas in the BTT instance
struct btt {
struct gendisk *btt_disk;
struct request_queue *btt_queue;
struct list_head arena_list;
struct dentry *debugfs_dir;
struct nd_btt *nd_btt;
u64 nlba;
unsigned long long rawsize;
u32 lbasize;
u32 sector_size;
struct nd_region *nd_region;
struct mutex init_lock;
int init_state;
int num_arenas;
......@@ -348,7 +348,8 @@ struct device *nd_btt_create(struct nd_region *nd_region)
u64 nd_btt_sb_checksum(struct btt_sb *btt_sb)
u64 sum, sum_save;
u64 sum;
__le64 sum_save;
sum_save = btt_sb->checksum;
btt_sb->checksum = 0;
......@@ -76,6 +76,30 @@ static bool is_namespace_io(struct device *dev)
return dev ? dev->type == &namespace_io_device_type : false;
const char *nvdimm_namespace_disk_name(struct nd_namespace_common *ndns,
char *name)
struct nd_region *nd_region = to_nd_region(ndns->dev.parent);
const char *suffix = "";
if (ndns->claim && is_nd_btt(ndns->claim))
suffix = "s";
if (is_namespace_pmem(&ndns->dev) || is_namespace_io(&ndns->dev))
sprintf(name, "pmem%d%s", nd_region->id, suffix);
else if (is_namespace_blk(&ndns->dev)) {
struct nd_namespace_blk *nsblk;
nsblk = to_nd_namespace_blk(&ndns->dev);
sprintf(name, "ndblk%d.%d%s", nd_region->id, nsblk->id, suffix);
} else {
return NULL;
return name;
static ssize_t nstype_show(struct device *dev,
struct device_attribute *attr, char *buf)
......@@ -20,6 +20,12 @@
#include "label.h"
enum {
* Limits the maximum number of block apertures a dimm can
* support and is an input to the geometry/on-disk-format of a
* BTT instance
......@@ -75,6 +81,11 @@ static inline struct nd_namespace_index *to_next_namespace_index(
for (res = (ndd)->dpa.child, next = res ? res->sibling : NULL; \
res; res = next, next = next ? next->sibling : NULL)
struct nd_percpu_lane {
int count;
spinlock_t lock;
struct nd_region {
struct device dev;
struct ida ns_ida;
......@@ -84,9 +95,10 @@ struct nd_region {
u16 ndr_mappings;
u64 ndr_size;
u64 ndr_start;
int id;
int id, num_lanes;
void *provider_data;
struct nd_interleave_set *nd_set;
struct nd_percpu_lane __percpu *lane;
struct nd_mapping mapping[0];
......@@ -100,9 +112,11 @@ static inline unsigned nd_inc_seq(unsigned seq)
return next[seq & 3];
struct btt;
struct nd_btt {
struct device dev;
struct nd_namespace_common *ndns;
struct btt *btt;
unsigned long lbasize;
u8 *uuid;
int id;
......@@ -157,6 +171,8 @@ static inline struct device *nd_btt_create(struct nd_region *nd_region)
struct nd_region *to_nd_region(struct device *dev);
unsigned int nd_region_acquire_lane(struct nd_region *nd_region);
void nd_region_release_lane(struct nd_region *nd_region, unsigned int lane);
int nd_region_to_nstype(struct nd_region *nd_region);
int nd_region_register_namespaces(struct nd_region *nd_region, int *err);
u64 nd_region_interleave_set_cookie(struct nd_region *nd_region);
......@@ -172,4 +188,8 @@ struct resource *nvdimm_allocate_dpa(struct nvdimm_drvdata *ndd,
resource_size_t n);
resource_size_t nvdimm_namespace_capacity(struct nd_namespace_common *ndns);
struct nd_namespace_common *nvdimm_namespace_common_probe(struct device *dev);
int nvdimm_namespace_attach_btt(struct nd_namespace_common *ndns);
int nvdimm_namespace_detach_btt(struct nd_namespace_common *ndns);
const char *nvdimm_namespace_disk_name(struct nd_namespace_common *ndns,
char *name);
#endif /* __ND_H__ */
......@@ -160,7 +160,6 @@ static void pmem_detach_disk(struct pmem_device *pmem)
static int pmem_attach_disk(struct nd_namespace_common *ndns,
struct pmem_device *pmem)
struct nd_region *nd_region = to_nd_region(ndns->dev.parent);
struct gendisk *disk;
pmem->pmem_queue = blk_alloc_queue(GFP_KERNEL);
......@@ -183,7 +182,7 @@ static int pmem_attach_disk(struct nd_namespace_common *ndns,
disk->private_data = pmem;
disk->queue = pmem->pmem_queue;
disk->flags = GENHD_FL_EXT_DEVT;
sprintf(disk->disk_name, "pmem%d", nd_region->id);
nvdimm_namespace_disk_name(ndns, disk->disk_name);
disk->driverfs_dev = &ndns->dev;
set_capacity(disk, pmem->size >> 9);
pmem->pmem_disk = disk;
......@@ -211,17 +210,6 @@ static int pmem_rw_bytes(struct nd_namespace_common *ndns,
return 0;
static int nvdimm_namespace_attach_btt(struct nd_namespace_common *ndns)
/* TODO */
return -ENXIO;
static void nvdimm_namespace_detach_btt(struct nd_namespace_common *ndns)
/* TODO */
static void pmem_free(struct pmem_device *pmem)
......@@ -10,6 +10,7 @@
* General Public License for more details.
#include <linux/cpumask.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/nd.h>
......@@ -18,10 +19,21 @@
static int nd_region_probe(struct device *dev)
int err;
static unsigned long once;
struct nd_region_namespaces *num_ns;
struct nd_region *nd_region = to_nd_region(dev);
int rc = nd_region_register_namespaces(nd_region, &err);
if (nd_region->num_lanes > num_online_cpus()
&& nd_region->num_lanes < num_possible_cpus()
&& !test_and_set_bit(0, &once)) {
dev_info(dev, "online cpus (%d) < concurrent i/o lanes (%d) < possible cpus (%d)\n",
num_online_cpus(), nd_region->num_lanes,
dev_info(dev, "setting nr_cpus=%d may yield better libnvdimm device performance\n",
num_ns = devm_kzalloc(dev, sizeof(*num_ns), GFP_KERNEL);
if (!num_ns)
return -ENOMEM;
......@@ -32,6 +32,7 @@ static void nd_region_release(struct device *dev)
ida_simple_remove(&region_ida, nd_region->id);
......@@ -531,13 +532,66 @@ void *nd_region_provider_data(struct nd_region *nd_region)
* nd_region_acquire_lane - allocate and lock a lane
* @nd_region: region id and number of lanes possible
* A lane correlates to a BLK-data-window and/or a log slot in the BTT.
* We optimize for the common case where there are 256 lanes, one
* per-cpu. For larger systems we need to lock to share lanes. For now
* this implementation assumes the cost of maintaining an allocator for
* free lanes is on the order of the lock hold time, so it implements a
* static lane = cpu % num_lanes mapping.
* In the case of a BTT instance on top of a BLK namespace a lane may be
* acquired recursively. We lock on the first instance.
* In the case of a BTT instance on top of PMEM, we only acquire a lane
* for the BTT metadata updates.
unsigned int nd_region_acquire_lane(struct nd_region *nd_region)
unsigned int cpu, lane;
cpu = get_cpu();
if (nd_region->num_lanes < nr_cpu_ids) {
struct nd_percpu_lane *ndl_lock, *ndl_count;
lane = cpu % nd_region->num_lanes;
ndl_count = per_cpu_ptr(nd_region->lane, cpu);
ndl_lock = per_cpu_ptr(nd_region->lane, lane);
if (ndl_count->count++ == 0)
} else
lane = cpu;
return lane;
void nd_region_release_lane(struct nd_region *nd_region, unsigned int lane)
if (nd_region->num_lanes < nr_cpu_ids) {
unsigned int cpu = get_cpu();
struct nd_percpu_lane *ndl_lock, *ndl_count;
ndl_count = per_cpu_ptr(nd_region->lane, cpu);
ndl_lock = per_cpu_ptr(nd_region->lane, lane);
if (--ndl_count->count == 0)
static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
struct nd_region_desc *ndr_desc, struct device_type *dev_type,
const char *caller)
struct nd_region *nd_region;
struct device *dev;
u16 i;
unsigned int i;
for (i = 0; i < ndr_desc->num_mappings; i++) {
struct nd_mapping *nd_mapping = &ndr_desc->nd_mapping[i];
......@@ -557,9 +611,19 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
if (!nd_region)
return NULL;
nd_region->id = ida_simple_get(&region_ida, 0, 0, GFP_KERNEL);
if (nd_region->id < 0) {
return NULL;
if (nd_region->id < 0)
goto err_id;
nd_region->lane = alloc_percpu(struct nd_percpu_lane);
if (!nd_region->lane)
goto err_percpu;
for (i = 0; i < nr_cpu_ids; i++) {
struct nd_percpu_lane *ndl;
ndl = per_cpu_ptr(nd_region->lane, i);
ndl->count = 0;
memcpy(nd_region->mapping, ndr_desc->nd_mapping,
......@@ -573,6 +637,7 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
nd_region->ndr_mappings = ndr_desc->num_mappings;
nd_region->provider_data = ndr_desc->provider_data;
nd_region->nd_set = ndr_desc->nd_set;
nd_region->num_lanes = ndr_desc->num_lanes;
dev = &nd_region->dev;
......@@ -585,11 +650,18 @@ static struct nd_region *nd_region_create(struct nvdimm_bus *nvdimm_bus,
return nd_region;
ida_simple_remove(&region_ida, nd_region->id);
return NULL;
struct nd_region *nvdimm_pmem_region_create(struct nvdimm_bus *nvdimm_bus,
struct nd_region_desc *ndr_desc)
ndr_desc->num_lanes = ND_MAX_LANES;
return nd_region_create(nvdimm_bus, ndr_desc, &nd_pmem_device_type,
......@@ -600,6 +672,7 @@ struct nd_region *nvdimm_blk_region_create(struct nvdimm_bus *nvdimm_bus,
if (ndr_desc->num_mappings > 1)
return NULL;
ndr_desc->num_lanes = min(ndr_desc->num_lanes, ND_MAX_LANES);
return nd_region_create(nvdimm_bus, ndr_desc, &nd_blk_device_type,
......@@ -608,6 +681,7 @@ EXPORT_SYMBOL_GPL(nvdimm_blk_region_create);
struct nd_region *nvdimm_volatile_region_create(struct nvdimm_bus *nvdimm_bus,
struct nd_region_desc *ndr_desc)
ndr_desc->num_lanes = ND_MAX_LANES;
return nd_region_create(nvdimm_bus, ndr_desc, &nd_volatile_device_type,
......@@ -85,6 +85,7 @@ struct nd_region_desc {
const struct attribute_group **attr_groups;
struct nd_interleave_set *nd_set;
void *provider_data;
int num_lanes;
struct nvdimm_bus;
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