On 7/16/20 8:41 AM, Coly Li wrote:
On 2020/7/16 14:15, Hannes Reinecke wrote:
On 7/15/20 4:30 PM, colyli@xxxxxxx wrote:
From: Coly Li <colyli@xxxxxxx>
The large bucket feature is to extend bucket_size from 16bit to 32bit.
When create cache device on zoned device (e.g. zoned NVMe SSD), making
a single bucket cover one or more zones of the zoned device is the
simplest way to support zoned device as cache by bcache.
But current maximum bucket size is 16MB and a typical zone size of zoned
device is 256MB, this is the major motiviation to extend bucket size to
a larger bit width.
This patch is the basic and first change to support large bucket size,
the major changes it makes are,
- Add BCH_FEATURE_INCOMPAT_LARGE_BUCKET for the large bucket feature,
INCOMPAT means it introduces incompatible on-disk format change.
- Add BCH_FEATURE_INCOMPAT_FUNCS(large_bucket, LARGE_BUCKET) routines.
- Adds __le32 bucket_size_hi into struct cache_sb_disk at offset 0x8d0
for the on-disk super block format.
- For the in-memory super block struct cache_sb, member bucket_size is
extended from __u16 to __32.
- Add get_bucket_size() to combine the bucket_size and bucket_size_hi
from struct cache_sb_disk into an unsigned int value.
Since we already have large bucket size helpers meta_bucket_pages(),
meta_bucket_bytes() and alloc_meta_bucket_pages(), they make sure when
bucket size > 8MB, the memory allocation for bcache meta data bucket
won't fail no matter how large the bucket size extended. So these meta
data buckets are handled properly when the bucket size width increase
from 16bit to 32bit, we don't need to worry about them.
Signed-off-by: Coly Li <colyli@xxxxxxx>
---
drivers/md/bcache/alloc.c | 2 +-
drivers/md/bcache/features.c | 22 ++++++++++++++++++++++
drivers/md/bcache/features.h | 9 ++++++---
drivers/md/bcache/movinggc.c | 4 ++--
drivers/md/bcache/super.c | 23 +++++++++++++++++++----
include/uapi/linux/bcache.h | 3 ++-
6 files changed, 52 insertions(+), 11 deletions(-)
create mode 100644 drivers/md/bcache/features.c
diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index a1df0d95151c..52035a78d836 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -87,7 +87,7 @@ void bch_rescale_priorities(struct cache_set *c, int
sectors)
{
struct cache *ca;
struct bucket *b;
- unsigned int next = c->nbuckets * c->sb.bucket_size / 1024;
+ unsigned long next = c->nbuckets * c->sb.bucket_size / 1024;
unsigned int i;
int r;
diff --git a/drivers/md/bcache/features.c
b/drivers/md/bcache/features.c
new file mode 100644
index 000000000000..ba53944bb390
--- /dev/null
+++ b/drivers/md/bcache/features.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Feature set bits and string conversion.
+ * Inspired by ext4's features compat/incompat/ro_compat related code.
+ *
+ * Copyright 2020 Coly Li <colyli@xxxxxxx>
+ *
+ */
+#include <linux/bcache.h>
+#include "bcache.h"
+
+struct feature {
+ int compat;
+ unsigned int mask;
+ const char *string;
+};
+
+static struct feature feature_list[] = {
+ {BCH_FEATURE_INCOMPAT, BCH_FEATURE_INCOMPAT_LARGE_BUCKET,
+ "large_bucket"},
+ {0, 0, 0 },
+};
diff --git a/drivers/md/bcache/features.h b/drivers/md/bcache/features.h
index ae7df37b9862..dca052cf5203 100644
--- a/drivers/md/bcache/features.h
+++ b/drivers/md/bcache/features.h
@@ -11,9 +11,13 @@
#define BCH_FEATURE_INCOMPAT 2
#define BCH_FEATURE_TYPE_MASK 0x03
+/* Feature set definition */
+/* Incompat feature set */
+#define BCH_FEATURE_INCOMPAT_LARGE_BUCKET 0x0001 /* 32bit bucket
size */
+
#define BCH_FEATURE_COMPAT_SUUP 0
#define BCH_FEATURE_RO_COMPAT_SUUP 0
-#define BCH_FEATURE_INCOMPAT_SUUP 0
+#define BCH_FEATURE_INCOMPAT_SUUP BCH_FEATURE_INCOMPAT_LARGE_BUCKET
#define BCH_HAS_COMPAT_FEATURE(sb, mask) \
((sb)->feature_compat & (mask))
@@ -22,8 +26,6 @@
#define BCH_HAS_INCOMPAT_FEATURE(sb, mask) \
((sb)->feature_incompat & (mask))
-/* Feature set definition */
-
#define BCH_FEATURE_COMPAT_FUNCS(name, flagname) \
static inline int bch_has_feature_##name(struct cache_sb *sb) \
{ \
@@ -75,4 +77,5 @@ static inline void bch_clear_feature_##name(struct
cache_sb *sb) \
~BCH##_FEATURE_INCOMPAT_##flagname; \
}
+BCH_FEATURE_INCOMPAT_FUNCS(large_bucket, LARGE_BUCKET);
#endif
diff --git a/drivers/md/bcache/movinggc.c b/drivers/md/bcache/movinggc.c
index b7dd2d75f58c..5872d6470470 100644
--- a/drivers/md/bcache/movinggc.c
+++ b/drivers/md/bcache/movinggc.c
@@ -206,8 +206,8 @@ void bch_moving_gc(struct cache_set *c)
mutex_lock(&c->bucket_lock);
for_each_cache(ca, c, i) {
- unsigned int sectors_to_move = 0;
- unsigned int reserve_sectors = ca->sb.bucket_size *
+ unsigned long sectors_to_move = 0;
+ unsigned long reserve_sectors = ca->sb.bucket_size *
fifo_used(&ca->free[RESERVE_MOVINGGC]);
ca->heap.used = 0;
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 02901d0ae8e2..e0da52f8e8c9 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -60,6 +60,17 @@ struct workqueue_struct *bch_journal_wq;
/* Superblock */
+static unsigned int get_bucket_size(struct cache_sb *sb, struct
cache_sb_disk *s)
+{
+ unsigned int bucket_size = le16_to_cpu(s->bucket_size);
+
+ if (sb->version >= BCACHE_SB_VERSION_CDEV_WITH_FEATURES &&
+ bch_has_feature_large_bucket(sb))
+ bucket_size |= le32_to_cpu(s->bucket_size_hi) << 16;
+
+ return bucket_size;
+}
+
static const char *read_super_common(struct cache_sb *sb, struct
block_device *bdev,
struct cache_sb_disk *s)
{
That is a bit unfortunate; bucket_size_hi is 32 bits, so we might end up
with an overflow here if bucket_size_hi is larger that USHRT_MAX.
In bcache-tools, the maximum value of bucket_size is restricted to
UINT_MAX in make_bcache(),
case 'b':
bucket_size =
hatoi_validate(optarg, "bucket size", UINT_MAX);
break;
So the overflow won't happen if people use bcache program to make the
cache device.
If people want to modify bucket_size_hi themselves, in
read_super_common(), there are several checks to make sure the hacked
cache_sb->bucket_size composed from the hacked bucket_size_hi won't mess
up whole kernel,
1) should be power of 2
if (!is_power_of_2(sb->bucket_size))
2) should large than page size
if (sb->bucket_size < PAGE_SECTORS)
3) should match sb->nbuckets
if (get_capacity(bdev->bd_disk) <
sb->bucket_size * sb->nbuckets)
4) no overlap with super block
if (sb->first_bucket * sb->bucket_size < 16)
Therefore the overflow won't happen, and even happen by hacking it won't
panic kernel.
So to avoid overflow either make bucket_size_hi 16 bit, too, or define
this feature such that the original bucket_size field is ignored and
just the new size field is used.
Now cache_sb_disk is for on-disk format, it contains 16bit bucket_size
and 32bit bucket_size_hi. cache_sb is for in-memory object only, it
simply has a 32bit bucket_size.
Indeed I planed to set cache_sb->bucket_size to be uint64_t, but I feel
people won't use bucket size > 1TB, and finally make it to be a 32bit value.
I will add more code comments to explain why there won't be overflow in
get_bucket_size() because user space tool limits the maximum size.
So why not make bucket_size_hi 16-bit?
That would clear up the ambiguity, and you wouldn't need to add comments ...
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
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