bcache: remove bcache device self-defined readahead

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: Victor Westerhuis <victor@westerhu.is>
Reported-by: Vojtech Pavlik <vojtech@suse.cz>
Reported-and-tested-by: Rolf Fokkens <rolf@rolffokkens.nl>
Reported-and-tested-by: Thorsten Knabe <linux@thorsten-knabe.de>
Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Cc: Nix <nix@esperi.org.uk>
Cc: Takashi Iwai <tiwai@suse.com>
Link: https://lore.kernel.org/r/20210607125052.21277-2-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 0a4551e..5fc989a 100644 (file)
--- 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 29c2317..ab8ff18 100644 (file)
--- 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 503aafe..4c7ee5f 100644 (file)
--- 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 abfaabf..ca4f435 100644 (file)
--- 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 cc89f31..05ac1d6 100644 (file)
--- 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,