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Date:   Thu, 28 Jun 2018 22:43:29 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Michal Hocko <mhocko@kernel.org>
cc:     jing xia <jing.xia.mail@gmail.com>,
        Mike Snitzer <snitzer@redhat.com>, agk@redhat.com,
        dm-devel@redhat.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: dm bufio: Reduce dm_bufio_lock contention
In-Reply-To: <20180625145733.GP28965@dhcp22.suse.cz>
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On Mon, 25 Jun 2018, Michal Hocko wrote:

> On Mon 25-06-18 10:42:30, Mikulas Patocka wrote:
> > 
> > 
> > On Mon, 25 Jun 2018, Michal Hocko wrote:
> > 
> > > > And the throttling in dm-bufio prevents kswapd from making forward 
> > > > progress, causing this situation...
> > > 
> > > Which is what we have PF_THROTTLE_LESS for. Geez, do we have to go in
> > > circles like that? Are you even listening?
> > > 
> > > [...]
> > > 
> > > > And so what do you want to do to prevent block drivers from sleeping?
> > > 
> > > use the existing means we have.
> > > -- 
> > > Michal Hocko
> > > SUSE Labs
> > 
> > So - do you want this patch?
> > 
> > There is no behavior difference between changing the allocator (so that it 
> > implies PF_THROTTLE_LESS for block drivers) and chaning all the block 
> > drivers to explicitly set PF_THROTTLE_LESS.
> 
> As long as you can reliably detect those users. And using gfp_mask is

You can detect them if __GFP_IO is not set and __GFP_NORETRY is set. You 
can grep the kernel for __GFP_NORETRY to find all the users.

> about the worst way to achieve that because users tend to be creative
> when it comes to using gfp mask. PF_THROTTLE_LESS in general is a
> way to tell the allocator that _you_ are the one to help the reclaim by
> cleaning data.

But using PF_LESS_THROTTLE explicitly adds more lines of code than 
implying PF_LESS_THROTTLE in the allocator.

> > But if you insist that the allocator can't be changed, we have to repeat 
> > the same code over and over again in the block drivers.
> 
> I am not familiar with the patched code but mempool change at least
> makes sense (bvec_alloc seems to fallback to mempool which then makes
> sense as well). If others in md/ do the same thing
> 
> I would just use current_restore_flags rather than open code it.
> 
> Thanks!
> -- 
> Michal Hocko
> SUSE Labs

So, do you accept this patch?

Mikulas


From: Mikulas Patocka <mpatocka@redhat.com>
Subject: [PATCH] mm: set PF_LESS_THROTTLE when allocating memory for i/o

When doing __GFP_NORETRY allocation, the system may sleep in
wait_iff_congested if there are too many dirty pages. Unfortunatelly this
sleeping may slow down kswapd, preventing it from doing writeback and
resolving the congestion.

This patch fixes it by setting PF_LESS_THROTTLE when allocating memory for
block device drivers.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

---
 block/bio.c                   |    4 ++++
 drivers/md/dm-bufio.c         |   14 +++++++++++---
 drivers/md/dm-crypt.c         |    8 ++++++++
 drivers/md/dm-integrity.c     |    4 ++++
 drivers/md/dm-kcopyd.c        |    3 +++
 drivers/md/dm-verity-target.c |    4 ++++
 drivers/md/dm-writecache.c    |    4 ++++
 mm/mempool.c                  |    4 ++++
 8 files changed, 42 insertions(+), 3 deletions(-)

Index: linux-2.6/mm/mempool.c
===================================================================
--- linux-2.6.orig/mm/mempool.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/mm/mempool.c	2018-06-29 03:47:16.270000000 +0200
@@ -369,6 +369,7 @@ void *mempool_alloc(mempool_t *pool, gfp
 	unsigned long flags;
 	wait_queue_entry_t wait;
 	gfp_t gfp_temp;
+	unsigned old_flags;
 
 	VM_WARN_ON_ONCE(gfp_mask & __GFP_ZERO);
 	might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM);
@@ -381,7 +382,10 @@ void *mempool_alloc(mempool_t *pool, gfp
 
 repeat_alloc:
 
+	old_flags = current->flags & PF_LESS_THROTTLE;
+	current->flags |= PF_LESS_THROTTLE;
 	element = pool->alloc(gfp_temp, pool->pool_data);
+	current_restore_flags(old_flags, PF_LESS_THROTTLE);
 	if (likely(element != NULL))
 		return element;
 
Index: linux-2.6/block/bio.c
===================================================================
--- linux-2.6.orig/block/bio.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/block/bio.c	2018-06-29 03:47:16.270000000 +0200
@@ -217,6 +217,7 @@ fallback:
 	} else {
 		struct biovec_slab *bvs = bvec_slabs + *idx;
 		gfp_t __gfp_mask = gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_IO);
+		unsigned old_flags;
 
 		/*
 		 * Make this allocation restricted and don't dump info on
@@ -229,7 +230,10 @@ fallback:
 		 * Try a slab allocation. If this fails and __GFP_DIRECT_RECLAIM
 		 * is set, retry with the 1-entry mempool
 		 */
+		old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
 		bvl = kmem_cache_alloc(bvs->slab, __gfp_mask);
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
 		if (unlikely(!bvl && (gfp_mask & __GFP_DIRECT_RECLAIM))) {
 			*idx = BVEC_POOL_MAX;
 			goto fallback;
Index: linux-2.6/drivers/md/dm-bufio.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-bufio.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/drivers/md/dm-bufio.c	2018-06-29 03:47:16.270000000 +0200
@@ -356,6 +356,7 @@ static void __cache_size_refresh(void)
 static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
 			       unsigned char *data_mode)
 {
+	void *ptr;
 	if (unlikely(c->slab_cache != NULL)) {
 		*data_mode = DATA_MODE_SLAB;
 		return kmem_cache_alloc(c->slab_cache, gfp_mask);
@@ -363,9 +364,14 @@ static void *alloc_buffer_data(struct dm
 
 	if (c->block_size <= KMALLOC_MAX_SIZE &&
 	    gfp_mask & __GFP_NORETRY) {
+		unsigned old_flags;
 		*data_mode = DATA_MODE_GET_FREE_PAGES;
-		return (void *)__get_free_pages(gfp_mask,
+		old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
+		ptr = (void *)__get_free_pages(gfp_mask,
 						c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
+		return ptr;
 	}
 
 	*data_mode = DATA_MODE_VMALLOC;
@@ -381,8 +387,10 @@ static void *alloc_buffer_data(struct dm
 	 */
 	if (gfp_mask & __GFP_NORETRY) {
 		unsigned noio_flag = memalloc_noio_save();
-		void *ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
-
+		unsigned old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
+		ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
 		memalloc_noio_restore(noio_flag);
 		return ptr;
 	}
Index: linux-2.6/drivers/md/dm-integrity.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-integrity.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/drivers/md/dm-integrity.c	2018-06-29 03:47:16.270000000 +0200
@@ -1318,6 +1318,7 @@ static void integrity_metadata(struct wo
 	int r;
 
 	if (ic->internal_hash) {
+		unsigned old_flags;
 		struct bvec_iter iter;
 		struct bio_vec bv;
 		unsigned digest_size = crypto_shash_digestsize(ic->internal_hash);
@@ -1331,8 +1332,11 @@ static void integrity_metadata(struct wo
 		if (unlikely(ic->mode == 'R'))
 			goto skip_io;
 
+		old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
 		checksums = kmalloc((PAGE_SIZE >> SECTOR_SHIFT >> ic->sb->log2_sectors_per_block) * ic->tag_size + extra_space,
 				    GFP_NOIO | __GFP_NORETRY | __GFP_NOWARN);
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
 		if (!checksums)
 			checksums = checksums_onstack;
 
Index: linux-2.6/drivers/md/dm-kcopyd.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-kcopyd.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/drivers/md/dm-kcopyd.c	2018-06-29 03:47:16.270000000 +0200
@@ -245,7 +245,10 @@ static int kcopyd_get_pages(struct dm_kc
 	*pages = NULL;
 
 	do {
+		unsigned old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
 		pl = alloc_pl(__GFP_NOWARN | __GFP_NORETRY | __GFP_KSWAPD_RECLAIM);
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
 		if (unlikely(!pl)) {
 			/* Use reserved pages */
 			pl = kc->pages;
Index: linux-2.6/drivers/md/dm-verity-target.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-verity-target.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/drivers/md/dm-verity-target.c	2018-06-29 03:47:16.280000000 +0200
@@ -596,9 +596,13 @@ no_prefetch_cluster:
 static void verity_submit_prefetch(struct dm_verity *v, struct dm_verity_io *io)
 {
 	struct dm_verity_prefetch_work *pw;
+	unsigned old_flags;
 
+	old_flags = current->flags & PF_LESS_THROTTLE;
+	current->flags |= PF_LESS_THROTTLE;
 	pw = kmalloc(sizeof(struct dm_verity_prefetch_work),
 		GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+	current_restore_flags(old_flags, PF_LESS_THROTTLE);
 
 	if (!pw)
 		return;
Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/drivers/md/dm-writecache.c	2018-06-29 03:47:16.280000000 +0200
@@ -1473,6 +1473,7 @@ static void __writecache_writeback_pmem(
 	unsigned max_pages;
 
 	while (wbl->size) {
+		unsigned old_flags;
 		wbl->size--;
 		e = container_of(wbl->list.prev, struct wc_entry, lru);
 		list_del(&e->lru);
@@ -1486,6 +1487,8 @@ static void __writecache_writeback_pmem(
 		bio_set_dev(&wb->bio, wc->dev->bdev);
 		wb->bio.bi_iter.bi_sector = read_original_sector(wc, e);
 		wb->page_offset = PAGE_SIZE;
+		old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
 		if (max_pages <= WB_LIST_INLINE ||
 		    unlikely(!(wb->wc_list = kmalloc(max_pages * sizeof(struct wc_entry *),
 						     GFP_NOIO | __GFP_NORETRY |
@@ -1493,6 +1496,7 @@ static void __writecache_writeback_pmem(
 			wb->wc_list = wb->wc_list_inline;
 			max_pages = WB_LIST_INLINE;
 		}
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
 
 		BUG_ON(!wc_add_block(wb, e, GFP_NOIO));
 
Index: linux-2.6/drivers/md/dm-crypt.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-crypt.c	2018-06-29 03:47:16.290000000 +0200
+++ linux-2.6/drivers/md/dm-crypt.c	2018-06-29 03:47:16.280000000 +0200
@@ -2181,12 +2181,16 @@ static void *crypt_page_alloc(gfp_t gfp_
 {
 	struct crypt_config *cc = pool_data;
 	struct page *page;
+	unsigned old_flags;
 
 	if (unlikely(percpu_counter_compare(&cc->n_allocated_pages, dm_crypt_pages_per_client) >= 0) &&
 	    likely(gfp_mask & __GFP_NORETRY))
 		return NULL;
 
+	old_flags = current->flags & PF_LESS_THROTTLE;
+	current->flags |= PF_LESS_THROTTLE;
 	page = alloc_page(gfp_mask);
+	current_restore_flags(old_flags, PF_LESS_THROTTLE);
 	if (likely(page != NULL))
 		percpu_counter_add(&cc->n_allocated_pages, 1);
 
@@ -2893,7 +2897,10 @@ static int crypt_map(struct dm_target *t
 
 	if (cc->on_disk_tag_size) {
 		unsigned tag_len = cc->on_disk_tag_size * (bio_sectors(bio) >> cc->sector_shift);
+		unsigned old_flags;
 
+		old_flags = current->flags & PF_LESS_THROTTLE;
+		current->flags |= PF_LESS_THROTTLE;
 		if (unlikely(tag_len > KMALLOC_MAX_SIZE) ||
 		    unlikely(!(io->integrity_metadata = kmalloc(tag_len,
 				GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN)))) {
@@ -2902,6 +2909,7 @@ static int crypt_map(struct dm_target *t
 			io->integrity_metadata = mempool_alloc(&cc->tag_pool, GFP_NOIO);
 			io->integrity_metadata_from_pool = true;
 		}
+		current_restore_flags(old_flags, PF_LESS_THROTTLE);
 	}
 
 	if (crypt_integrity_aead(cc))