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* [PATCH v5 1/2] bcache: remove bcache device self-defined readahead
@ 2021-05-31 15:31 Coly Li
  2021-05-31 15:31 ` [PATCH v5 2/2] bcache: avoid oversized read request in cache missing code path Coly Li
  0 siblings, 1 reply; 7+ messages in thread
From: Coly Li @ 2021-05-31 15:31 UTC (permalink / raw)
  To: linux-bcache
  Cc: linux-block, linux-kernel, Coly Li, Alexander Ullrich,
	Diego Ercolani, Jan Szubiak, Marco Rebhan, Matthias Ferdinand,
	Thorsten Knabe, Victor Westerhuis, Vojtech Pavlik, stable,
	Christoph Hellwig, Kent Overstreet, Nix, Takashi Iwai

For read cache missing, bcache defines a readahead size for the read I/O
request to the backing device for the missing data. This readahead size
is initialized to 0, and almost no one uses it to avoid unnecessary read
amplifying onto backing device and write amplifying onto cache device.
Considering upper layer file system code has readahead logic allready
and works fine with readahead_cache_policy sysfile interface, we don't
have to keep bcache self-defined readahead anymore.

This patch removes the bcache self-defined readahead for cache missing
request for backing device, and the readahead sysfs file interfaces are
removed as well.

This is the preparation for next patch to fix potential kernel panic due
to oversized request in a simpler method.

Reported-by: Alexander Ullrich <ealex1979@gmail.com>
Reported-by: Diego Ercolani <diego.ercolani@gmail.com>
Reported-by: Jan Szubiak <jan.szubiak@linuxpolska.pl>
Reported-by: Marco Rebhan <me@dblsaiko.net>
Reported-by: Matthias Ferdinand <bcache@mfedv.net>
Reported-by: Thorsten Knabe <linux@thorsten-knabe.de>
Reported-by: Victor Westerhuis <victor@westerhu.is>
Reported-by: Vojtech Pavlik <vojtech@suse.cz>
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Cc: Christoph Hellwig <hch@lst.de>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Nix <nix@esperi.org.uk>
Cc: Takashi Iwai <tiwai@suse.com>
---
Changlog,
v1, the initial version by hint from  Christoph Hellwig.

 drivers/md/bcache/bcache.h  |  1 -
 drivers/md/bcache/request.c | 13 +------------
 drivers/md/bcache/stats.c   | 14 --------------
 drivers/md/bcache/stats.h   |  1 -
 drivers/md/bcache/sysfs.c   |  4 ----
 5 files changed, 1 insertion(+), 32 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 0a4551e165ab..5fc989a6d452 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -364,7 +364,6 @@ struct cached_dev {
 
 	/* The rest of this all shows up in sysfs */
 	unsigned int		sequential_cutoff;
-	unsigned int		readahead;
 
 	unsigned int		io_disable:1;
 	unsigned int		verify:1;
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 29c231758293..ab8ff18df32a 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -880,7 +880,6 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s,
 				 struct bio *bio, unsigned int sectors)
 {
 	int ret = MAP_CONTINUE;
-	unsigned int reada = 0;
 	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
 	struct bio *miss, *cache_bio;
 
@@ -892,14 +891,7 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s,
 		goto out_submit;
 	}
 
-	if (!(bio->bi_opf & REQ_RAHEAD) &&
-	    !(bio->bi_opf & (REQ_META|REQ_PRIO)) &&
-	    s->iop.c->gc_stats.in_use < CUTOFF_CACHE_READA)
-		reada = min_t(sector_t, dc->readahead >> 9,
-			      get_capacity(bio->bi_bdev->bd_disk) -
-			      bio_end_sector(bio));
-
-	s->insert_bio_sectors = min(sectors, bio_sectors(bio) + reada);
+	s->insert_bio_sectors = min(sectors, bio_sectors(bio));
 
 	s->iop.replace_key = KEY(s->iop.inode,
 				 bio->bi_iter.bi_sector + s->insert_bio_sectors,
@@ -933,9 +925,6 @@ static int cached_dev_cache_miss(struct btree *b, struct search *s,
 	if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO))
 		goto out_put;
 
-	if (reada)
-		bch_mark_cache_readahead(s->iop.c, s->d);
-
 	s->cache_miss	= miss;
 	s->iop.bio	= cache_bio;
 	bio_get(cache_bio);
diff --git a/drivers/md/bcache/stats.c b/drivers/md/bcache/stats.c
index 503aafe188dc..4c7ee5fedb9d 100644
--- a/drivers/md/bcache/stats.c
+++ b/drivers/md/bcache/stats.c
@@ -46,7 +46,6 @@ read_attribute(cache_misses);
 read_attribute(cache_bypass_hits);
 read_attribute(cache_bypass_misses);
 read_attribute(cache_hit_ratio);
-read_attribute(cache_readaheads);
 read_attribute(cache_miss_collisions);
 read_attribute(bypassed);
 
@@ -64,7 +63,6 @@ SHOW(bch_stats)
 		    DIV_SAFE(var(cache_hits) * 100,
 			     var(cache_hits) + var(cache_misses)));
 
-	var_print(cache_readaheads);
 	var_print(cache_miss_collisions);
 	sysfs_hprint(bypassed,	var(sectors_bypassed) << 9);
 #undef var
@@ -86,7 +84,6 @@ static struct attribute *bch_stats_files[] = {
 	&sysfs_cache_bypass_hits,
 	&sysfs_cache_bypass_misses,
 	&sysfs_cache_hit_ratio,
-	&sysfs_cache_readaheads,
 	&sysfs_cache_miss_collisions,
 	&sysfs_bypassed,
 	NULL
@@ -113,7 +110,6 @@ void bch_cache_accounting_clear(struct cache_accounting *acc)
 	acc->total.cache_misses = 0;
 	acc->total.cache_bypass_hits = 0;
 	acc->total.cache_bypass_misses = 0;
-	acc->total.cache_readaheads = 0;
 	acc->total.cache_miss_collisions = 0;
 	acc->total.sectors_bypassed = 0;
 }
@@ -145,7 +141,6 @@ static void scale_stats(struct cache_stats *stats, unsigned long rescale_at)
 		scale_stat(&stats->cache_misses);
 		scale_stat(&stats->cache_bypass_hits);
 		scale_stat(&stats->cache_bypass_misses);
-		scale_stat(&stats->cache_readaheads);
 		scale_stat(&stats->cache_miss_collisions);
 		scale_stat(&stats->sectors_bypassed);
 	}
@@ -168,7 +163,6 @@ static void scale_accounting(struct timer_list *t)
 	move_stat(cache_misses);
 	move_stat(cache_bypass_hits);
 	move_stat(cache_bypass_misses);
-	move_stat(cache_readaheads);
 	move_stat(cache_miss_collisions);
 	move_stat(sectors_bypassed);
 
@@ -209,14 +203,6 @@ void bch_mark_cache_accounting(struct cache_set *c, struct bcache_device *d,
 	mark_cache_stats(&c->accounting.collector, hit, bypass);
 }
 
-void bch_mark_cache_readahead(struct cache_set *c, struct bcache_device *d)
-{
-	struct cached_dev *dc = container_of(d, struct cached_dev, disk);
-
-	atomic_inc(&dc->accounting.collector.cache_readaheads);
-	atomic_inc(&c->accounting.collector.cache_readaheads);
-}
-
 void bch_mark_cache_miss_collision(struct cache_set *c, struct bcache_device *d)
 {
 	struct cached_dev *dc = container_of(d, struct cached_dev, disk);
diff --git a/drivers/md/bcache/stats.h b/drivers/md/bcache/stats.h
index abfaabf7e7fc..ca4f435f7216 100644
--- a/drivers/md/bcache/stats.h
+++ b/drivers/md/bcache/stats.h
@@ -7,7 +7,6 @@ struct cache_stat_collector {
 	atomic_t cache_misses;
 	atomic_t cache_bypass_hits;
 	atomic_t cache_bypass_misses;
-	atomic_t cache_readaheads;
 	atomic_t cache_miss_collisions;
 	atomic_t sectors_bypassed;
 };
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index cc89f3156d1a..05ac1d6fbbf3 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -137,7 +137,6 @@ rw_attribute(io_disable);
 rw_attribute(discard);
 rw_attribute(running);
 rw_attribute(label);
-rw_attribute(readahead);
 rw_attribute(errors);
 rw_attribute(io_error_limit);
 rw_attribute(io_error_halflife);
@@ -260,7 +259,6 @@ SHOW(__bch_cached_dev)
 	var_printf(partial_stripes_expensive,	"%u");
 
 	var_hprint(sequential_cutoff);
-	var_hprint(readahead);
 
 	sysfs_print(running,		atomic_read(&dc->running));
 	sysfs_print(state,		states[BDEV_STATE(&dc->sb)]);
@@ -365,7 +363,6 @@ STORE(__cached_dev)
 	sysfs_strtoul_clamp(sequential_cutoff,
 			    dc->sequential_cutoff,
 			    0, UINT_MAX);
-	d_strtoi_h(readahead);
 
 	if (attr == &sysfs_clear_stats)
 		bch_cache_accounting_clear(&dc->accounting);
@@ -538,7 +535,6 @@ static struct attribute *bch_cached_dev_files[] = {
 	&sysfs_running,
 	&sysfs_state,
 	&sysfs_label,
-	&sysfs_readahead,
 #ifdef CONFIG_BCACHE_DEBUG
 	&sysfs_verify,
 	&sysfs_bypass_torture_test,
-- 
2.26.2


^ permalink raw reply	[flat|nested] 7+ messages in thread
* [PATCH 0/2] bcache fixes for Linux v5.13-rc6
@ 2021-06-07 10:35 Coly Li
  2021-06-07 10:35 ` [PATCH v5 2/2] bcache: avoid oversized read request in cache missing code path Coly Li
  0 siblings, 1 reply; 7+ messages in thread
From: Coly Li @ 2021-06-07 10:35 UTC (permalink / raw)
  To: axboe; +Cc: linux-bcache, linux-block, linux-kernel, Coly Li

Hi Jens,

This series is important for recent reported bcache panic partially
triggered by recent bio changes since Linux v5.12.

Current fix is 5th version since the first effort, it might not be
perfect yet, but it survives from different workloads from Rolf,
Thorsten and me for more than 1 week in total.

Considering many people are waiting for a stable enough fix and it is
kind of such fix. Please take them for Linux v5.13-rc6.

Thank you in advance for taking care of them.

Coly Li
---

Coly Li (2):
  bcache: remove bcache device self-defined readahead
  bcache: avoid oversized read request in cache missing code path

 drivers/md/bcache/bcache.h  |  1 -
 drivers/md/bcache/request.c | 19 ++++++-------------
 drivers/md/bcache/stats.c   | 14 --------------
 drivers/md/bcache/stats.h   |  1 -
 drivers/md/bcache/sysfs.c   |  4 ----
 5 files changed, 6 insertions(+), 33 deletions(-)

-- 
2.26.2


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2021-06-07 12:32 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-31 15:31 [PATCH v5 1/2] bcache: remove bcache device self-defined readahead Coly Li
2021-05-31 15:31 ` [PATCH v5 2/2] bcache: avoid oversized read request in cache missing code path Coly Li
2021-06-07 10:35 [PATCH 0/2] bcache fixes for Linux v5.13-rc6 Coly Li
2021-06-07 10:35 ` [PATCH v5 2/2] bcache: avoid oversized read request in cache missing code path Coly Li
2021-06-07 11:06   ` Christoph Hellwig
2021-06-07 11:55     ` Coly Li
2021-06-07 12:08       ` Christoph Hellwig
2021-06-07 12:31         ` Coly Li

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