linux/mm/bounce.c
Darrick J. Wong ffecfd1a72 block: optionally snapshot page contents to provide stable pages during write
This provides a band-aid to provide stable page writes on jbd without
needing to backport the fixed locking and page writeback bit handling
schemes of jbd2.  The band-aid works by using bounce buffers to snapshot
page contents instead of waiting.

For those wondering about the ext3 bandage -- fixing the jbd locking
(which was done as part of ext4dev years ago) is a lot of surgery, and
setting PG_writeback on data pages when we actually hold the page lock
dropped ext3 performance by nearly an order of magnitude.  If we're
going to migrate iscsi and raid to use stable page writes, the
complaints about high latency will likely return.  We might as well
centralize their page snapshotting thing to one place.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Tested-by: Andy Lutomirski <luto@amacapital.net>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
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 17:22:20 -08:00

342 lines
7.5 KiB
C

/* bounce buffer handling for block devices
*
* - Split from highmem.c
*/
#include <linux/mm.h>
#include <linux/export.h>
#include <linux/swap.h>
#include <linux/gfp.h>
#include <linux/bio.h>
#include <linux/pagemap.h>
#include <linux/mempool.h>
#include <linux/blkdev.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/highmem.h>
#include <linux/bootmem.h>
#include <asm/tlbflush.h>
#include <trace/events/block.h>
#define POOL_SIZE 64
#define ISA_POOL_SIZE 16
static mempool_t *page_pool, *isa_page_pool;
#if defined(CONFIG_HIGHMEM) || defined(CONFIG_NEED_BOUNCE_POOL)
static __init int init_emergency_pool(void)
{
#if defined(CONFIG_HIGHMEM) && !defined(CONFIG_MEMORY_HOTPLUG)
if (max_pfn <= max_low_pfn)
return 0;
#endif
page_pool = mempool_create_page_pool(POOL_SIZE, 0);
BUG_ON(!page_pool);
printk("bounce pool size: %d pages\n", POOL_SIZE);
return 0;
}
__initcall(init_emergency_pool);
#endif
#ifdef CONFIG_HIGHMEM
/*
* highmem version, map in to vec
*/
static void bounce_copy_vec(struct bio_vec *to, unsigned char *vfrom)
{
unsigned long flags;
unsigned char *vto;
local_irq_save(flags);
vto = kmap_atomic(to->bv_page);
memcpy(vto + to->bv_offset, vfrom, to->bv_len);
kunmap_atomic(vto);
local_irq_restore(flags);
}
#else /* CONFIG_HIGHMEM */
#define bounce_copy_vec(to, vfrom) \
memcpy(page_address((to)->bv_page) + (to)->bv_offset, vfrom, (to)->bv_len)
#endif /* CONFIG_HIGHMEM */
/*
* allocate pages in the DMA region for the ISA pool
*/
static void *mempool_alloc_pages_isa(gfp_t gfp_mask, void *data)
{
return mempool_alloc_pages(gfp_mask | GFP_DMA, data);
}
/*
* gets called "every" time someone init's a queue with BLK_BOUNCE_ISA
* as the max address, so check if the pool has already been created.
*/
int init_emergency_isa_pool(void)
{
if (isa_page_pool)
return 0;
isa_page_pool = mempool_create(ISA_POOL_SIZE, mempool_alloc_pages_isa,
mempool_free_pages, (void *) 0);
BUG_ON(!isa_page_pool);
printk("isa bounce pool size: %d pages\n", ISA_POOL_SIZE);
return 0;
}
/*
* Simple bounce buffer support for highmem pages. Depending on the
* queue gfp mask set, *to may or may not be a highmem page. kmap it
* always, it will do the Right Thing
*/
static void copy_to_high_bio_irq(struct bio *to, struct bio *from)
{
unsigned char *vfrom;
struct bio_vec *tovec, *fromvec;
int i;
__bio_for_each_segment(tovec, to, i, 0) {
fromvec = from->bi_io_vec + i;
/*
* not bounced
*/
if (tovec->bv_page == fromvec->bv_page)
continue;
/*
* fromvec->bv_offset and fromvec->bv_len might have been
* modified by the block layer, so use the original copy,
* bounce_copy_vec already uses tovec->bv_len
*/
vfrom = page_address(fromvec->bv_page) + tovec->bv_offset;
bounce_copy_vec(tovec, vfrom);
flush_dcache_page(tovec->bv_page);
}
}
static void bounce_end_io(struct bio *bio, mempool_t *pool, int err)
{
struct bio *bio_orig = bio->bi_private;
struct bio_vec *bvec, *org_vec;
int i;
if (test_bit(BIO_EOPNOTSUPP, &bio->bi_flags))
set_bit(BIO_EOPNOTSUPP, &bio_orig->bi_flags);
/*
* free up bounce indirect pages used
*/
__bio_for_each_segment(bvec, bio, i, 0) {
org_vec = bio_orig->bi_io_vec + i;
if (bvec->bv_page == org_vec->bv_page)
continue;
dec_zone_page_state(bvec->bv_page, NR_BOUNCE);
mempool_free(bvec->bv_page, pool);
}
bio_endio(bio_orig, err);
bio_put(bio);
}
static void bounce_end_io_write(struct bio *bio, int err)
{
bounce_end_io(bio, page_pool, err);
}
static void bounce_end_io_write_isa(struct bio *bio, int err)
{
bounce_end_io(bio, isa_page_pool, err);
}
static void __bounce_end_io_read(struct bio *bio, mempool_t *pool, int err)
{
struct bio *bio_orig = bio->bi_private;
if (test_bit(BIO_UPTODATE, &bio->bi_flags))
copy_to_high_bio_irq(bio_orig, bio);
bounce_end_io(bio, pool, err);
}
static void bounce_end_io_read(struct bio *bio, int err)
{
__bounce_end_io_read(bio, page_pool, err);
}
static void bounce_end_io_read_isa(struct bio *bio, int err)
{
__bounce_end_io_read(bio, isa_page_pool, err);
}
#ifdef CONFIG_NEED_BOUNCE_POOL
static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
{
struct page *page;
struct backing_dev_info *bdi;
struct address_space *mapping;
struct bio_vec *from;
int i;
if (bio_data_dir(bio) != WRITE)
return 0;
if (!bdi_cap_stable_pages_required(&q->backing_dev_info))
return 0;
/*
* Based on the first page that has a valid mapping, decide whether or
* not we have to employ bounce buffering to guarantee stable pages.
*/
bio_for_each_segment(from, bio, i) {
page = from->bv_page;
mapping = page_mapping(page);
if (!mapping)
continue;
bdi = mapping->backing_dev_info;
return mapping->host->i_sb->s_flags & MS_SNAP_STABLE;
}
return 0;
}
#else
static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
{
return 0;
}
#endif /* CONFIG_NEED_BOUNCE_POOL */
static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
mempool_t *pool, int force)
{
struct page *page;
struct bio *bio = NULL;
int i, rw = bio_data_dir(*bio_orig);
struct bio_vec *to, *from;
bio_for_each_segment(from, *bio_orig, i) {
page = from->bv_page;
/*
* is destination page below bounce pfn?
*/
if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
continue;
/*
* irk, bounce it
*/
if (!bio) {
unsigned int cnt = (*bio_orig)->bi_vcnt;
bio = bio_alloc(GFP_NOIO, cnt);
memset(bio->bi_io_vec, 0, cnt * sizeof(struct bio_vec));
}
to = bio->bi_io_vec + i;
to->bv_page = mempool_alloc(pool, q->bounce_gfp);
to->bv_len = from->bv_len;
to->bv_offset = from->bv_offset;
inc_zone_page_state(to->bv_page, NR_BOUNCE);
if (rw == WRITE) {
char *vto, *vfrom;
flush_dcache_page(from->bv_page);
vto = page_address(to->bv_page) + to->bv_offset;
vfrom = kmap(from->bv_page) + from->bv_offset;
memcpy(vto, vfrom, to->bv_len);
kunmap(from->bv_page);
}
}
/*
* no pages bounced
*/
if (!bio)
return;
trace_block_bio_bounce(q, *bio_orig);
/*
* at least one page was bounced, fill in possible non-highmem
* pages
*/
__bio_for_each_segment(from, *bio_orig, i, 0) {
to = bio_iovec_idx(bio, i);
if (!to->bv_page) {
to->bv_page = from->bv_page;
to->bv_len = from->bv_len;
to->bv_offset = from->bv_offset;
}
}
bio->bi_bdev = (*bio_orig)->bi_bdev;
bio->bi_flags |= (1 << BIO_BOUNCED);
bio->bi_sector = (*bio_orig)->bi_sector;
bio->bi_rw = (*bio_orig)->bi_rw;
bio->bi_vcnt = (*bio_orig)->bi_vcnt;
bio->bi_idx = (*bio_orig)->bi_idx;
bio->bi_size = (*bio_orig)->bi_size;
if (pool == page_pool) {
bio->bi_end_io = bounce_end_io_write;
if (rw == READ)
bio->bi_end_io = bounce_end_io_read;
} else {
bio->bi_end_io = bounce_end_io_write_isa;
if (rw == READ)
bio->bi_end_io = bounce_end_io_read_isa;
}
bio->bi_private = *bio_orig;
*bio_orig = bio;
}
void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
{
int must_bounce;
mempool_t *pool;
/*
* Data-less bio, nothing to bounce
*/
if (!bio_has_data(*bio_orig))
return;
must_bounce = must_snapshot_stable_pages(q, *bio_orig);
/*
* for non-isa bounce case, just check if the bounce pfn is equal
* to or bigger than the highest pfn in the system -- in that case,
* don't waste time iterating over bio segments
*/
if (!(q->bounce_gfp & GFP_DMA)) {
if (queue_bounce_pfn(q) >= blk_max_pfn && !must_bounce)
return;
pool = page_pool;
} else {
BUG_ON(!isa_page_pool);
pool = isa_page_pool;
}
/*
* slow path
*/
__blk_queue_bounce(q, bio_orig, pool, must_bounce);
}
EXPORT_SYMBOL(blk_queue_bounce);