Re: [PATCH v3 13/16] bcache: add bucket_size_hi into struct cache_sb_disk for large bucket

Hannes Reinecke
2020-07-16T06:15:10Z

On 7/15/20 4:30 PM, colyli@suse.de wrote:
> From: Coly Li <colyli@suse.de>
>
> 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@suse.de>
> ---
> 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@suse.de>
> + *
> + */
> +#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.

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.

Cheers,

Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@suse.de +49 911 74053 688
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