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dm thin: remap the bios in a cell immediately

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This use of direct submission in process_prepared_mapping() reduces
latency for submitting bios in a cell by avoiding adding those bios to
the deferred list and waiting for the next iteration of the worker.

But this direct submission exposes the potential for a race between
releasing a cell and incrementing deferred set.  Fix this by introducing
dm_cell_visit_release() and refactoring inc_remap_and_issue_cell()
accordingly.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Joe Thornber 2014-10-10 15:27:16 +01:00 committed by Mike Snitzer
parent a374bb217b
commit 2d759a46b4
3 changed files with 84 additions and 30 deletions
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14
drivers/md/dm-bio-prison.c
View File

@ -241,6 +241,20 @@ void dm_cell_error(struct dm_bio_prison *prison,
}
EXPORT_SYMBOL_GPL(dm_cell_error);
void dm_cell_visit_release(struct dm_bio_prison *prison,
void (*visit_fn)(void *, struct dm_bio_prison_cell *),
void *context,
struct dm_bio_prison_cell *cell)
{
unsigned long flags;
spin_lock_irqsave(&prison->lock, flags);
visit_fn(context, cell);
rb_erase(&cell->node, &prison->cells);
spin_unlock_irqrestore(&prison->lock, flags);
}
EXPORT_SYMBOL_GPL(dm_cell_visit_release);
/*----------------------------------------------------------------*/
#define DEFERRED_SET_SIZE 64

8
drivers/md/dm-bio-prison.h
View File

@ -89,6 +89,14 @@ void dm_cell_release_no_holder(struct dm_bio_prison *prison,
void dm_cell_error(struct dm_bio_prison *prison,
struct dm_bio_prison_cell *cell, int error);
/*
* Visits the cell and then releases. Guarantees no new inmates are
* inserted between the visit and release.
*/
void dm_cell_visit_release(struct dm_bio_prison *prison,
void (*visit_fn)(void *, struct dm_bio_prison_cell *),
void *context, struct dm_bio_prison_cell *cell);
/*----------------------------------------------------------------*/
/*

92
drivers/md/dm-thin.c
View File

@ -343,6 +343,15 @@ static void cell_release(struct pool *pool,
dm_bio_prison_free_cell(pool->prison, cell);
}
static void cell_visit_release(struct pool *pool,
void (*fn)(void *, struct dm_bio_prison_cell *),
void *context,
struct dm_bio_prison_cell *cell)
{
dm_cell_visit_release(pool->prison, fn, context, cell);
dm_bio_prison_free_cell(pool->prison, cell);
}
static void cell_release_no_holder(struct pool *pool,
struct dm_bio_prison_cell *cell,
struct bio_list *bios)
@ -697,22 +706,8 @@ static void overwrite_endio(struct bio *bio, int err)
*/
/*
* This sends the bios in the cell back to the deferred_bios list.
*/
static void cell_defer(struct thin_c *tc, struct dm_bio_prison_cell *cell)
{
struct pool *pool = tc->pool;
unsigned long flags;
spin_lock_irqsave(&tc->lock, flags);
cell_release(pool, cell, &tc->deferred_bio_list);
spin_unlock_irqrestore(&tc->lock, flags);
wake_worker(pool);
}
/*
* Same as cell_defer above, except it omits the original holder of the cell.
* This sends the bios in the cell, except the original holder, back
* to the deferred_bios list.
*/
static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *cell)
{
@ -728,24 +723,58 @@ static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *c
static void thin_defer_bio(struct thin_c *tc, struct bio *bio);
struct remap_info {
struct thin_c *tc;
struct bio_list defer_bios;
struct bio_list issue_bios;
};
static void __inc_remap_and_issue_cell(void *context,
struct dm_bio_prison_cell *cell)
{
struct remap_info *info = context;
struct bio *bio;
while ((bio = bio_list_pop(&cell->bios))) {
if (bio->bi_rw & (REQ_DISCARD | REQ_FLUSH | REQ_FUA))
bio_list_add(&info->defer_bios, bio);
else {
inc_all_io_entry(info->tc->pool, bio);
/*
* We can't issue the bios with the bio prison lock
* held, so we add them to a list to issue on
* return from this function.
*/
bio_list_add(&info->issue_bios, bio);
}
}
}
static void inc_remap_and_issue_cell(struct thin_c *tc,
struct dm_bio_prison_cell *cell,
dm_block_t block)
{
struct bio *bio;
struct bio_list bios;
struct remap_info info;
bio_list_init(&bios);
cell_release_no_holder(tc->pool, cell, &bios);
info.tc = tc;
bio_list_init(&info.defer_bios);
bio_list_init(&info.issue_bios);
while ((bio = bio_list_pop(&bios))) {
if (bio->bi_rw & (REQ_DISCARD | REQ_FLUSH | REQ_FUA))
thin_defer_bio(tc, bio);
else {
inc_all_io_entry(tc->pool, bio);
remap_and_issue(tc, bio, block);
}
}
/*
* We have to be careful to inc any bios we're about to issue
* before the cell is released, and avoid a race with new bios
* being added to the cell.
*/
cell_visit_release(tc->pool, __inc_remap_and_issue_cell,
&info, cell);
while ((bio = bio_list_pop(&info.defer_bios)))
thin_defer_bio(tc, bio);
while ((bio = bio_list_pop(&info.issue_bios)))
remap_and_issue(info.tc, bio, block);
}
static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
@ -796,10 +825,13 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
* the bios in the cell.
*/
if (bio) {
cell_defer_no_holder(tc, m->cell);
inc_remap_and_issue_cell(tc, m->cell, m->data_block);
bio_endio(bio, 0);
} else
cell_defer(tc, m->cell);
} else {
inc_all_io_entry(tc->pool, m->cell->holder);
remap_and_issue(tc, m->cell->holder, m->data_block);
inc_remap_and_issue_cell(tc, m->cell, m->data_block);
}
out:
list_del(&m->list);