On Wed, Feb 10 2021 at 11:50am -0500, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > Hi > > Here I'm sending the patch that fixes swapping to dm-crypt. > > The logic that limits the number of in-progress I/Os was moved to generic > device mapper. A dm target can activate it by setting ti->limit_swap. The > actual limit can be set in /sys/module/dm_mod/parameters/swap_ios. > > This patch only limits swap bios (those with REQ_SWAP set). I don't limit > other bios, because limiting them causes performance degradation due to > cache line bouncing when taking the semaphore - and there are no reports > that non-swap I/O on dm crypt causes deadlocks. > > Mikulas > > > > From: Mikulas Patocka <mpatocka@xxxxxxxxxx> > > The system would deadlock when swapping to a dm-crypt device. The reason > is that for each incoming write bio, dm-crypt allocates memory that holds > encrypted data. These excessive allocations exhaust all the memory and the > result is either deadlock or OOM trigger. > > This patch limits the number of in-flight swap bios, so that the memory > consumed by dm-crypt is limited. The limit is enforced if the target set > the "limit_swap" variable and if the bio has REQ_SWAP set. > > Non-swap bios are not affected becuase taking the semaphore would cause > performance degradation. > > This is similar to request-based drivers - they will also block when the > number of requests is over the limit. > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > > --- > drivers/md/dm-core.h | 4 ++ > drivers/md/dm-crypt.c | 1 > drivers/md/dm.c | 61 ++++++++++++++++++++++++++++++++++++++++++ > include/linux/device-mapper.h | 5 +++ > 4 files changed, 71 insertions(+) > > Index: linux-2.6/drivers/md/dm.c > =================================================================== > --- linux-2.6.orig/drivers/md/dm.c 2021-02-10 15:04:53.000000000 +0100 > +++ linux-2.6/drivers/md/dm.c 2021-02-10 16:29:04.000000000 +0100 > @@ -1271,6 +1307,15 @@ static blk_qc_t __map_bio(struct dm_targ > atomic_inc(&io->io_count); > sector = clone->bi_iter.bi_sector; > > + if (unlikely(swap_io_limit(ti, clone))) { > + struct mapped_device *md = io->md; > + int latch = get_swap_ios(); > + if (unlikely(latch != md->swap_ios)) { > + __set_swap_io_limit(md, latch); > + } Don't need these curly braces... > + down(&md->swap_ios_semaphore); > + } > + > r = ti->type->map(ti, clone); > switch (r) { > case DM_MAPIO_SUBMITTED: > @@ -1814,6 +1868,10 @@ static struct mapped_device *alloc_dev(i > init_waitqueue_head(&md->eventq); > init_completion(&md->kobj_holder.completion); > > + md->swap_ios = get_swap_ios(); > + sema_init(&md->swap_ios_semaphore, md->swap_ios); > + mutex_init(&md->swap_ios_lock); > + > md->disk->major = _major; > md->disk->first_minor = minor; > md->disk->fops = &dm_blk_dops; This is only applicable for bio-based DM. But probably not worth avoiding the setup for request-based... > @@ -3097,6 +3155,9 @@ MODULE_PARM_DESC(reserved_bio_based_ios, > module_param(dm_numa_node, int, S_IRUGO | S_IWUSR); > MODULE_PARM_DESC(dm_numa_node, "NUMA node for DM device memory allocations"); > > +module_param(swap_ios, int, S_IRUGO | S_IWUSR); > +MODULE_PARM_DESC(swap_ios, "The number of swap I/Os in flight"); > + Can you please rename this to modparam to "swap_bios"? And rename other variables/members, etc (e.g. "swap_bios_semaphore", "swap_bios_lock", etc)? > Index: linux-2.6/include/linux/device-mapper.h > =================================================================== > --- linux-2.6.orig/include/linux/device-mapper.h 2020-11-25 13:40:44.000000000 +0100 > +++ linux-2.6/include/linux/device-mapper.h 2021-02-10 15:52:54.000000000 +0100 > @@ -325,6 +325,11 @@ struct dm_target { > * whether or not its underlying devices have support. > */ > bool discards_supported:1; > + > + /* > + * Set if we need to limit the number of in-flight bios when swapping. > + */ > + bool limit_swap:1; > }; > > void *dm_per_bio_data(struct bio *bio, size_t data_size); Please rename to "limit_swap_bios". Other than these nits this looks good to me. Once you send v2 I can get it staged for 5.12. Thanks, Mike -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel