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bcache: introduce meta_bucket_pages() related helper routines

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Currently the in-memory meta data like c->uuids or c->disk_buckets
are allocated by alloc_bucket_pages(). The macro alloc_bucket_pages()
calls __get_free_pages() to allocated continuous pages with order
indicated by ilog2(bucket_pages(c)),
 #define alloc_bucket_pages(gfp, c)                      \
     ((void *) __get_free_pages(__GFP_ZERO|gfp, ilog2(bucket_pages(c))))

The maximum order is defined as MAX_ORDER, the default value is 11 (and
can be overwritten by CONFIG_FORCE_MAX_ZONEORDER). In bcache code the
maximum bucket size width is 16bits, this is restricted both by KEY_SIZE
size and bucket_size size from struct cache_sb_disk. The maximum 16bits
width and power-of-2 value is (1<<15) in unit of sector (512byte). It
means the maximum value of bucket size in bytes is (1<<24) bytes a.k.a
4096 pages.

When the bucket size is set to maximum permitted value, ilog2(4096) is
12, which exceeds the default maximum order __get_free_pages() can
accepted, the failed pages allocation will fail cache set registration
procedure and print a kernel oops message for the exceeded pages order.

This patch introduces meta_bucket_pages(), meta_bucket_bytes(), and
alloc_bucket_pages() helper routines. meta_bucket_pages() indicates the
maximum pages can be allocated to meta data bucket, meta_bucket_bytes()
indicates the according maximum bytes, and alloc_bucket_pages() does
the pages allocation for meta bucket. Because meta_bucket_pages()
chooses the smaller value among the bucket size and MAX_ORDER_NR_PAGES,
it still works when MAX_ORDER overwritten by CONFIG_FORCE_MAX_ZONEORDER.

Following patches will use these helper routines to decide maximum pages
can be allocated for different meta data buckets. If the bucket size is
larger than meta_bucket_bytes(), the bcache registration can continue to
success, just the space more than meta_bucket_bytes() inside the bucket
is wasted. Comparing bcache failed for large bucket size, wasting some
space for meta data buckets is acceptable at this moment.

Signed-off-by: Coly Li <colyli@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Coly Li 2020-07-25 20:00:30 +08:00 committed by Jens Axboe
parent 4c1ccd0896
commit de1fafab64
2 changed files with 23 additions and 0 deletions
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20
drivers/md/bcache/bcache.h
View File

@ -762,6 +762,26 @@ struct bbio {
#define bucket_bytes(c) ((c)->sb.bucket_size << 9)
#define block_bytes(c) ((c)->sb.block_size << 9)
static inline unsigned int meta_bucket_pages(struct cache_sb *sb)
{
unsigned int n, max_pages;
max_pages = min_t(unsigned int,
__rounddown_pow_of_two(USHRT_MAX) / PAGE_SECTORS,
MAX_ORDER_NR_PAGES);
n = sb->bucket_size / PAGE_SECTORS;
if (n > max_pages)
n = max_pages;
return n;
}
static inline unsigned int meta_bucket_bytes(struct cache_sb *sb)
{
return meta_bucket_pages(sb) << PAGE_SHIFT;
}
#define prios_per_bucket(c) \
((bucket_bytes(c) - sizeof(struct prio_set)) / \
sizeof(struct bucket_disk))

3
drivers/md/bcache/super.c
View File

@ -1829,6 +1829,9 @@ void bch_cache_set_unregister(struct cache_set *c)
#define alloc_bucket_pages(gfp, c) \
((void *) __get_free_pages(__GFP_ZERO|__GFP_COMP|gfp, ilog2(bucket_pages(c))))
#define alloc_meta_bucket_pages(gfp, sb) \
((void *) __get_free_pages(__GFP_ZERO|__GFP_COMP|gfp, ilog2(meta_bucket_pages(sb))))
struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
{
int iter_size;