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loop: Limit the number of requests in the bio list 

Currently there is not limitation of number of requests in the loop bio
list. This can lead into some nasty situations when the caller spawns
tons of bio requests taking huge amount of memory. This is even more
obvious with discard where blkdev_issue_discard() will submit all bios
for the range and wait for them to finish afterwards. On really big loop
devices and slow backing file system this can lead to OOM situation as
reported by Dave Chinner.

With this patch we will wait in loop_make_request() if the number of
bios in the loop bio list would exceed 'nr_congestion_on'.
We'll wake up the process as we process the bios form the list. Some
threshold hysteresis is in place to avoid high frequency oscillation.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reported-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Lukas Czerner 2012-11-30 11:42:41 +01:00 committed by Jens Axboe
parent eed8c02e68
commit 7b5a35225b
2 changed files with 13 additions and 0 deletions
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10
drivers/block/loop.c
View File

@ -463,6 +463,7 @@ out:
*/
static void loop_add_bio(struct loop_device *lo, struct bio *bio)
{
lo->lo_bio_count++;
bio_list_add(&lo->lo_bio_list, bio);
}
@ -471,6 +472,7 @@ static void loop_add_bio(struct loop_device *lo, struct bio *bio)
*/
static struct bio *loop_get_bio(struct loop_device *lo)
{
lo->lo_bio_count--;
return bio_list_pop(&lo->lo_bio_list);
}
@ -489,6 +491,10 @@ static void loop_make_request(struct request_queue *q, struct bio *old_bio)
goto out;
if (unlikely(rw == WRITE && (lo->lo_flags & LO_FLAGS_READ_ONLY)))
goto out;
if (lo->lo_bio_count >= q->nr_congestion_on)
wait_event_lock_irq(lo->lo_req_wait,
lo->lo_bio_count < q->nr_congestion_off,
lo->lo_lock);
loop_add_bio(lo, old_bio);
wake_up(&lo->lo_event);
spin_unlock_irq(&lo->lo_lock);
@ -546,6 +552,8 @@ static int loop_thread(void *data)
continue;
spin_lock_irq(&lo->lo_lock);
bio = loop_get_bio(lo);
if (lo->lo_bio_count < lo->lo_queue->nr_congestion_off)
wake_up(&lo->lo_req_wait);
spin_unlock_irq(&lo->lo_lock);
BUG_ON(!bio);
@ -873,6 +881,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
lo->transfer = transfer_none;
lo->ioctl = NULL;
lo->lo_sizelimit = 0;
lo->lo_bio_count = 0;
lo->old_gfp_mask = mapping_gfp_mask(mapping);
mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
@ -1660,6 +1669,7 @@ static int loop_add(struct loop_device **l, int i)
lo->lo_number = i;
lo->lo_thread = NULL;
init_waitqueue_head(&lo->lo_event);
init_waitqueue_head(&lo->lo_req_wait);
spin_lock_init(&lo->lo_lock);
disk->major = LOOP_MAJOR;
disk->first_minor = i << part_shift;

3
include/linux/loop.h
View File

@ -53,10 +53,13 @@ struct loop_device {
spinlock_t lo_lock;
struct bio_list lo_bio_list;
unsigned int lo_bio_count;
int lo_state;
struct mutex lo_ctl_mutex;
struct task_struct *lo_thread;
wait_queue_head_t lo_event;
/* wait queue for incoming requests */
wait_queue_head_t lo_req_wait;
struct request_queue *lo_queue;
struct gendisk *lo_disk;