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
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
