Messages in this thread Patch in this message | | | Subject | Re: System freezes after OOM | From | Ondrej Kozina <> | Date | Thu, 14 Jul 2016 17:25:13 +0200 |
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On 07/14/2016 04:59 PM, Michal Hocko wrote: > On Thu 14-07-16 10:00:16, Mikulas Patocka wrote: >> >> >> On Thu, 14 Jul 2016, Michal Hocko wrote: >> >>> On Wed 13-07-16 11:02:15, Mikulas Patocka wrote: >> >>>>> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c >>>>> index 4f3cb3554944..0b806810efab 100644 >>>>> --- a/drivers/md/dm-crypt.c >>>>> +++ b/drivers/md/dm-crypt.c >>>>> @@ -1392,11 +1392,14 @@ static void kcryptd_async_done(struct crypto_async_request *async_req, >>>>> static void kcryptd_crypt(struct work_struct *work) >>>>> { >>>>> struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work); >>>>> + unsigned int pflags = current->flags; >>>>> >>>>> + current->flags |= PF_LESS_THROTTLE; >>>>> if (bio_data_dir(io->base_bio) == READ) >>>>> kcryptd_crypt_read_convert(io); >>>>> else >>>>> kcryptd_crypt_write_convert(io); >>>>> + tsk_restore_flags(current, pflags, PF_LESS_THROTTLE); >>>>> } >>>>> >>>>> static void kcryptd_queue_crypt(struct dm_crypt_io *io) >>>> >>>> ^^^ That fixes just one specific case - but there may be other threads >>>> doing mempool allocations in the device mapper subsystem - and you would >>>> need to mark all of them. >>> >>> Now that I am thinking about it some more. Are there any mempool users >>> which would actually want to be throttled? I would expect mempool users >>> are necessary to push IO through and throttle them sounds like a bad >>> decision in the first place but there might be other mempool users which >>> could cause issues. Anyway how about setting PF_LESS_THROTTLE >>> unconditionally inside mempool_alloc? Something like the following: >>> >>> diff --git a/mm/mempool.c b/mm/mempool.c >>> index 8f65464da5de..e21fb632983f 100644 >>> --- a/mm/mempool.c >>> +++ b/mm/mempool.c >>> @@ -310,7 +310,8 @@ EXPORT_SYMBOL(mempool_resize); >>> */ >>> void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask) >>> { >>> - void *element; >>> + unsigned int pflags = current->flags; >>> + void *element = NULL; >>> unsigned long flags; >>> wait_queue_t wait; >>> gfp_t gfp_temp; >>> @@ -327,6 +328,12 @@ void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask) >>> >>> gfp_temp = gfp_mask & ~(__GFP_DIRECT_RECLAIM|__GFP_IO); >>> >>> + /* >>> + * Make sure that the allocation doesn't get throttled during the >>> + * reclaim >>> + */ >>> + if (gfpflags_allow_blocking(gfp_mask)) >>> + current->flags |= PF_LESS_THROTTLE; >>> repeat_alloc: >>> if (likely(pool->curr_nr)) { >>> /* >>> @@ -339,7 +346,7 @@ void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask) >>> >>> element = pool->alloc(gfp_temp, pool->pool_data); >>> if (likely(element != NULL)) >>> - return element; >>> + goto out; >>> >>> spin_lock_irqsave(&pool->lock, flags); >>> if (likely(pool->curr_nr)) { >>> @@ -352,7 +359,7 @@ void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask) >>> * for debugging. >>> */ >>> kmemleak_update_trace(element); >>> - return element; >>> + goto out; >>> } >>> >>> /* >>> @@ -369,7 +376,7 @@ void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask) >>> /* We must not sleep if !__GFP_DIRECT_RECLAIM */ >>> if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) { >>> spin_unlock_irqrestore(&pool->lock, flags); >>> - return NULL; >>> + goto out; >>> } >>> >>> /* Let's wait for someone else to return an element to @pool */ >>> @@ -386,6 +393,10 @@ void *mempool_alloc(mempool_t *pool, gfp_t gfp_mask) >>> >>> finish_wait(&pool->wait, &wait); >>> goto repeat_alloc; >>> +out: >>> + if (gfpflags_allow_blocking(gfp_mask)) >>> + tsk_restore_flags(current, pflags, PF_LESS_THROTTLE); >>> + return element; >>> } >>> EXPORT_SYMBOL(mempool_alloc); >>> >> >> But it needs other changes to honor the PF_LESS_THROTTLE flag: >> >> static int current_may_throttle(void) >> { >> return !(current->flags & PF_LESS_THROTTLE) || >> current->backing_dev_info == NULL || >> bdi_write_congested(current->backing_dev_info); >> } >> --- if you set PF_LESS_THROTTLE, current_may_throttle may still return >> true if one of the other conditions is met. > > That is true but doesn't that mean that the device is congested and > waiting a bit is the right thing to do? > >> shrink_zone_memcg calls throttle_vm_writeout without checking >> PF_LESS_THROTTLE at all. > > Yes it doesn't call it because it relies on > global_dirty_limits()->domain_dirty_limits() to DTRT. It will give the > caller with PF_LESS_THROTTLE some boost wrt. all other writers. >
Not sure it'll help but I had to apply following patch to your original one. Without it it didn't work.
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index e248194..1616192 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1940,11 +1940,23 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb) return false; }
+static int current_may_throttle(void) +{ + if (current->flags & PF_LESS_THROTTLE) + return 0; + + return current->backing_dev_info == NULL || + bdi_write_congested(current->backing_dev_info); +} + void throttle_vm_writeout(gfp_t gfp_mask) { unsigned long background_thresh; unsigned long dirty_thresh;
+ if (!current_may_throttle()) + return; + for ( ; ; ) { global_dirty_limits(&background_thresh, &dirty_thresh); dirty_thresh = hard_dirty_limit(&global_wb_domain, dirty_thresh); Regards Ondra
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