linux/block/blk-integrity.c
Darrick J. Wong 7d311cdab6 bdi: allow block devices to say that they require stable page writes
This patchset ("stable page writes, part 2") makes some key
modifications to the original 'stable page writes' patchset.  First, it
provides creators (devices and filesystems) of a backing_dev_info a flag
that declares whether or not it is necessary to ensure that page
contents cannot change during writeout.  It is no longer assumed that
this is true of all devices (which was never true anyway).  Second, the
flag is used to relaxed the wait_on_page_writeback calls so that wait
only occurs if the device needs it.  Third, it fixes up the remaining
disk-backed filesystems to use this improved conditional-wait logic to
provide stable page writes on those filesystems.

It is hoped that (for people not using checksumming devices, anyway)
this patchset will give back unnecessary performance decreases since the
original stable page write patchset went into 3.0.  Sorry about not
fixing it sooner.

Complaints were registered by several people about the long write
latencies introduced by the original stable page write patchset.
Generally speaking, the kernel ought to allocate as little extra memory
as possible to facilitate writeout, but for people who simply cannot
wait, a second page stability strategy is (re)introduced: snapshotting
page contents.  The waiting behavior is still the default strategy; to
enable page snapshotting, a superblock flag (MS_SNAP_STABLE) must be
set.  This flag is used to bandaid^Henable stable page writeback on
ext3[1], and is not used anywhere else.

Given that there are already a few storage devices and network FSes that
have rolled their own page stability wait/page snapshot code, it would
be nice to move towards consolidating all of these.  It seems possible
that iscsi and raid5 may wish to use the new stable page write support
to enable zero-copy writeout.

Thank you to Jan Kara for helping fix a couple more filesystems.

Per Andrew Morton's request, here are the result of using dbench to measure
latencies on ext2:

3.8.0-rc3:
   Operation      Count    AvgLat    MaxLat
   ----------------------------------------
   WriteX        109347     0.028    59.817
   ReadX         347180     0.004     3.391
   Flush          15514    29.828   287.283

  Throughput 57.429 MB/sec  4 clients  4 procs  max_latency=287.290 ms

3.8.0-rc3 + patches:
   WriteX        105556     0.029     4.273
   ReadX         335004     0.005     4.112
   Flush          14982    30.540   298.634

  Throughput 55.4496 MB/sec  4 clients  4 procs  max_latency=298.650 ms

As you can see, for ext2 the maximum write latency decreases from ~60ms
on a laptop hard disk to ~4ms.  I'm not sure why the flush latencies
increase, though I suspect that being able to dirty pages faster gives
the flusher more work to do.

On ext4, the average write latency decreases as well as all the maximum
latencies:

3.8.0-rc3:
   WriteX         85624     0.152    33.078
   ReadX         272090     0.010    61.210
   Flush          12129    36.219   168.260

  Throughput 44.8618 MB/sec  4 clients  4 procs  max_latency=168.276 ms

3.8.0-rc3 + patches:
   WriteX         86082     0.141    30.928
   ReadX         273358     0.010    36.124
   Flush          12214    34.800   165.689

  Throughput 44.9941 MB/sec  4 clients  4 procs  max_latency=165.722 ms

XFS seems to exhibit similar latency improvements as ext2:

3.8.0-rc3:
   WriteX        125739     0.028   104.343
   ReadX         399070     0.005     4.115
   Flush          17851    25.004   131.390

  Throughput 66.0024 MB/sec  4 clients  4 procs  max_latency=131.406 ms

3.8.0-rc3 + patches:
   WriteX        123529     0.028     6.299
   ReadX         392434     0.005     4.287
   Flush          17549    25.120   188.687

  Throughput 64.9113 MB/sec  4 clients  4 procs  max_latency=188.704 ms

...and btrfs, just to round things out, also shows some latency
decreases:

3.8.0-rc3:
   WriteX         67122     0.083    82.355
   ReadX         212719     0.005     2.828
   Flush           9547    47.561   147.418

  Throughput 35.3391 MB/sec  4 clients  4 procs  max_latency=147.433 ms

3.8.0-rc3 + patches:
   WriteX         64898     0.101    71.631
   ReadX         206673     0.005     7.123
   Flush           9190    47.963   219.034

  Throughput 34.0795 MB/sec  4 clients  4 procs  max_latency=219.044 ms

Before this patchset, all filesystems would block, regardless of whether
or not it was necessary.  ext3 would wait, but still generate occasional
checksum errors.  The network filesystems were left to do their own
thing, so they'd wait too.

After this patchset, all the disk filesystems except ext3 and btrfs will
wait only if the hardware requires it.  ext3 (if necessary) snapshots
pages instead of blocking, and btrfs provides its own bdi so the mm will
never wait.  Network filesystems haven't been touched, so either they
provide their own wait code, or they don't block at all.  The blocking
behavior is back to what it was before 3.0 if you don't have a disk
requiring stable page writes.

This patchset has been tested on 3.8.0-rc3 on x64 with ext3, ext4, and
xfs.  I've spot-checked 3.8.0-rc4 and seem to be getting the same
results as -rc3.

[1] The alternative fixes to ext3 include fixing the locking order and
page bit handling like we did for ext4 (but then why not just use
ext4?), or setting PG_writeback so early that ext3 becomes extremely
slow.  I tried that, but the number of write()s I could initiate dropped
by nearly an order of magnitude.  That was a bit much even for the
author of the stable page series! :)

This patch:

Creates a per-backing-device flag that tracks whether or not pages must
be held immutable during writeout.  Eventually it will be used to waive
wait_for_page_writeback() if nothing requires stable pages.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-02-21 17:22:19 -08:00

452 lines
12 KiB
C

/*
* blk-integrity.c - Block layer data integrity extensions
*
* Copyright (C) 2007, 2008 Oracle Corporation
* Written by: Martin K. Petersen <martin.petersen@oracle.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version
* 2 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; see the file COPYING. If not, write to
* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139,
* USA.
*
*/
#include <linux/blkdev.h>
#include <linux/mempool.h>
#include <linux/bio.h>
#include <linux/scatterlist.h>
#include <linux/export.h>
#include <linux/slab.h>
#include "blk.h"
static struct kmem_cache *integrity_cachep;
static const char *bi_unsupported_name = "unsupported";
/**
* blk_rq_count_integrity_sg - Count number of integrity scatterlist elements
* @q: request queue
* @bio: bio with integrity metadata attached
*
* Description: Returns the number of elements required in a
* scatterlist corresponding to the integrity metadata in a bio.
*/
int blk_rq_count_integrity_sg(struct request_queue *q, struct bio *bio)
{
struct bio_vec *iv, *ivprv = NULL;
unsigned int segments = 0;
unsigned int seg_size = 0;
unsigned int i = 0;
bio_for_each_integrity_vec(iv, bio, i) {
if (ivprv) {
if (!BIOVEC_PHYS_MERGEABLE(ivprv, iv))
goto new_segment;
if (!BIOVEC_SEG_BOUNDARY(q, ivprv, iv))
goto new_segment;
if (seg_size + iv->bv_len > queue_max_segment_size(q))
goto new_segment;
seg_size += iv->bv_len;
} else {
new_segment:
segments++;
seg_size = iv->bv_len;
}
ivprv = iv;
}
return segments;
}
EXPORT_SYMBOL(blk_rq_count_integrity_sg);
/**
* blk_rq_map_integrity_sg - Map integrity metadata into a scatterlist
* @q: request queue
* @bio: bio with integrity metadata attached
* @sglist: target scatterlist
*
* Description: Map the integrity vectors in request into a
* scatterlist. The scatterlist must be big enough to hold all
* elements. I.e. sized using blk_rq_count_integrity_sg().
*/
int blk_rq_map_integrity_sg(struct request_queue *q, struct bio *bio,
struct scatterlist *sglist)
{
struct bio_vec *iv, *ivprv = NULL;
struct scatterlist *sg = NULL;
unsigned int segments = 0;
unsigned int i = 0;
bio_for_each_integrity_vec(iv, bio, i) {
if (ivprv) {
if (!BIOVEC_PHYS_MERGEABLE(ivprv, iv))
goto new_segment;
if (!BIOVEC_SEG_BOUNDARY(q, ivprv, iv))
goto new_segment;
if (sg->length + iv->bv_len > queue_max_segment_size(q))
goto new_segment;
sg->length += iv->bv_len;
} else {
new_segment:
if (!sg)
sg = sglist;
else {
sg->page_link &= ~0x02;
sg = sg_next(sg);
}
sg_set_page(sg, iv->bv_page, iv->bv_len, iv->bv_offset);
segments++;
}
ivprv = iv;
}
if (sg)
sg_mark_end(sg);
return segments;
}
EXPORT_SYMBOL(blk_rq_map_integrity_sg);
/**
* blk_integrity_compare - Compare integrity profile of two disks
* @gd1: Disk to compare
* @gd2: Disk to compare
*
* Description: Meta-devices like DM and MD need to verify that all
* sub-devices use the same integrity format before advertising to
* upper layers that they can send/receive integrity metadata. This
* function can be used to check whether two gendisk devices have
* compatible integrity formats.
*/
int blk_integrity_compare(struct gendisk *gd1, struct gendisk *gd2)
{
struct blk_integrity *b1 = gd1->integrity;
struct blk_integrity *b2 = gd2->integrity;
if (!b1 && !b2)
return 0;
if (!b1 || !b2)
return -1;
if (b1->sector_size != b2->sector_size) {
printk(KERN_ERR "%s: %s/%s sector sz %u != %u\n", __func__,
gd1->disk_name, gd2->disk_name,
b1->sector_size, b2->sector_size);
return -1;
}
if (b1->tuple_size != b2->tuple_size) {
printk(KERN_ERR "%s: %s/%s tuple sz %u != %u\n", __func__,
gd1->disk_name, gd2->disk_name,
b1->tuple_size, b2->tuple_size);
return -1;
}
if (b1->tag_size && b2->tag_size && (b1->tag_size != b2->tag_size)) {
printk(KERN_ERR "%s: %s/%s tag sz %u != %u\n", __func__,
gd1->disk_name, gd2->disk_name,
b1->tag_size, b2->tag_size);
return -1;
}
if (strcmp(b1->name, b2->name)) {
printk(KERN_ERR "%s: %s/%s type %s != %s\n", __func__,
gd1->disk_name, gd2->disk_name,
b1->name, b2->name);
return -1;
}
return 0;
}
EXPORT_SYMBOL(blk_integrity_compare);
int blk_integrity_merge_rq(struct request_queue *q, struct request *req,
struct request *next)
{
if (blk_integrity_rq(req) != blk_integrity_rq(next))
return -1;
if (req->nr_integrity_segments + next->nr_integrity_segments >
q->limits.max_integrity_segments)
return -1;
return 0;
}
EXPORT_SYMBOL(blk_integrity_merge_rq);
int blk_integrity_merge_bio(struct request_queue *q, struct request *req,
struct bio *bio)
{
int nr_integrity_segs;
struct bio *next = bio->bi_next;
bio->bi_next = NULL;
nr_integrity_segs = blk_rq_count_integrity_sg(q, bio);
bio->bi_next = next;
if (req->nr_integrity_segments + nr_integrity_segs >
q->limits.max_integrity_segments)
return -1;
req->nr_integrity_segments += nr_integrity_segs;
return 0;
}
EXPORT_SYMBOL(blk_integrity_merge_bio);
struct integrity_sysfs_entry {
struct attribute attr;
ssize_t (*show)(struct blk_integrity *, char *);
ssize_t (*store)(struct blk_integrity *, const char *, size_t);
};
static ssize_t integrity_attr_show(struct kobject *kobj, struct attribute *attr,
char *page)
{
struct blk_integrity *bi =
container_of(kobj, struct blk_integrity, kobj);
struct integrity_sysfs_entry *entry =
container_of(attr, struct integrity_sysfs_entry, attr);
return entry->show(bi, page);
}
static ssize_t integrity_attr_store(struct kobject *kobj,
struct attribute *attr, const char *page,
size_t count)
{
struct blk_integrity *bi =
container_of(kobj, struct blk_integrity, kobj);
struct integrity_sysfs_entry *entry =
container_of(attr, struct integrity_sysfs_entry, attr);
ssize_t ret = 0;
if (entry->store)
ret = entry->store(bi, page, count);
return ret;
}
static ssize_t integrity_format_show(struct blk_integrity *bi, char *page)
{
if (bi != NULL && bi->name != NULL)
return sprintf(page, "%s\n", bi->name);
else
return sprintf(page, "none\n");
}
static ssize_t integrity_tag_size_show(struct blk_integrity *bi, char *page)
{
if (bi != NULL)
return sprintf(page, "%u\n", bi->tag_size);
else
return sprintf(page, "0\n");
}
static ssize_t integrity_read_store(struct blk_integrity *bi,
const char *page, size_t count)
{
char *p = (char *) page;
unsigned long val = simple_strtoul(p, &p, 10);
if (val)
bi->flags |= INTEGRITY_FLAG_READ;
else
bi->flags &= ~INTEGRITY_FLAG_READ;
return count;
}
static ssize_t integrity_read_show(struct blk_integrity *bi, char *page)
{
return sprintf(page, "%d\n", (bi->flags & INTEGRITY_FLAG_READ) != 0);
}
static ssize_t integrity_write_store(struct blk_integrity *bi,
const char *page, size_t count)
{
char *p = (char *) page;
unsigned long val = simple_strtoul(p, &p, 10);
if (val)
bi->flags |= INTEGRITY_FLAG_WRITE;
else
bi->flags &= ~INTEGRITY_FLAG_WRITE;
return count;
}
static ssize_t integrity_write_show(struct blk_integrity *bi, char *page)
{
return sprintf(page, "%d\n", (bi->flags & INTEGRITY_FLAG_WRITE) != 0);
}
static struct integrity_sysfs_entry integrity_format_entry = {
.attr = { .name = "format", .mode = S_IRUGO },
.show = integrity_format_show,
};
static struct integrity_sysfs_entry integrity_tag_size_entry = {
.attr = { .name = "tag_size", .mode = S_IRUGO },
.show = integrity_tag_size_show,
};
static struct integrity_sysfs_entry integrity_read_entry = {
.attr = { .name = "read_verify", .mode = S_IRUGO | S_IWUSR },
.show = integrity_read_show,
.store = integrity_read_store,
};
static struct integrity_sysfs_entry integrity_write_entry = {
.attr = { .name = "write_generate", .mode = S_IRUGO | S_IWUSR },
.show = integrity_write_show,
.store = integrity_write_store,
};
static struct attribute *integrity_attrs[] = {
&integrity_format_entry.attr,
&integrity_tag_size_entry.attr,
&integrity_read_entry.attr,
&integrity_write_entry.attr,
NULL,
};
static const struct sysfs_ops integrity_ops = {
.show = &integrity_attr_show,
.store = &integrity_attr_store,
};
static int __init blk_dev_integrity_init(void)
{
integrity_cachep = kmem_cache_create("blkdev_integrity",
sizeof(struct blk_integrity),
0, SLAB_PANIC, NULL);
return 0;
}
subsys_initcall(blk_dev_integrity_init);
static void blk_integrity_release(struct kobject *kobj)
{
struct blk_integrity *bi =
container_of(kobj, struct blk_integrity, kobj);
kmem_cache_free(integrity_cachep, bi);
}
static struct kobj_type integrity_ktype = {
.default_attrs = integrity_attrs,
.sysfs_ops = &integrity_ops,
.release = blk_integrity_release,
};
bool blk_integrity_is_initialized(struct gendisk *disk)
{
struct blk_integrity *bi = blk_get_integrity(disk);
return (bi && bi->name && strcmp(bi->name, bi_unsupported_name) != 0);
}
EXPORT_SYMBOL(blk_integrity_is_initialized);
/**
* blk_integrity_register - Register a gendisk as being integrity-capable
* @disk: struct gendisk pointer to make integrity-aware
* @template: optional integrity profile to register
*
* Description: When a device needs to advertise itself as being able
* to send/receive integrity metadata it must use this function to
* register the capability with the block layer. The template is a
* blk_integrity struct with values appropriate for the underlying
* hardware. If template is NULL the new profile is allocated but
* not filled out. See Documentation/block/data-integrity.txt.
*/
int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
{
struct blk_integrity *bi;
BUG_ON(disk == NULL);
if (disk->integrity == NULL) {
bi = kmem_cache_alloc(integrity_cachep,
GFP_KERNEL | __GFP_ZERO);
if (!bi)
return -1;
if (kobject_init_and_add(&bi->kobj, &integrity_ktype,
&disk_to_dev(disk)->kobj,
"%s", "integrity")) {
kmem_cache_free(integrity_cachep, bi);
return -1;
}
kobject_uevent(&bi->kobj, KOBJ_ADD);
bi->flags |= INTEGRITY_FLAG_READ | INTEGRITY_FLAG_WRITE;
bi->sector_size = queue_logical_block_size(disk->queue);
disk->integrity = bi;
} else
bi = disk->integrity;
/* Use the provided profile as template */
if (template != NULL) {
bi->name = template->name;
bi->generate_fn = template->generate_fn;
bi->verify_fn = template->verify_fn;
bi->tuple_size = template->tuple_size;
bi->set_tag_fn = template->set_tag_fn;
bi->get_tag_fn = template->get_tag_fn;
bi->tag_size = template->tag_size;
} else
bi->name = bi_unsupported_name;
disk->queue->backing_dev_info.capabilities |= BDI_CAP_STABLE_WRITES;
return 0;
}
EXPORT_SYMBOL(blk_integrity_register);
/**
* blk_integrity_unregister - Remove block integrity profile
* @disk: disk whose integrity profile to deallocate
*
* Description: This function frees all memory used by the block
* integrity profile. To be called at device teardown.
*/
void blk_integrity_unregister(struct gendisk *disk)
{
struct blk_integrity *bi;
if (!disk || !disk->integrity)
return;
disk->queue->backing_dev_info.capabilities &= ~BDI_CAP_STABLE_WRITES;
bi = disk->integrity;
kobject_uevent(&bi->kobj, KOBJ_REMOVE);
kobject_del(&bi->kobj);
kobject_put(&bi->kobj);
disk->integrity = NULL;
}
EXPORT_SYMBOL(blk_integrity_unregister);