To support arbitrary page size for superblock,include 4K/8K/64K
currently, the off_set of SB_SECTOR should be a LCM(least common
multiple) and that is 64. I redefine macro SB_SECTOR and
BDEV_DATA_START_DEFAULT just as bellow patch showed:
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index ef567cd..1622f44 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -74,7 +74,7 @@ static const char *read_super(struct
cache_sb *sb, struct block_device *bdev,
{
const char *err;
struct cache_sb *s;
- struct buffer_head *bh = __bread(bdev, 1, SB_SIZE);
+ struct buffer_head *bh = __bread(bdev, 16, SB_SIZE);
unsigned i;
if (!bh)
diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
index 22b6ad3..eb948c8 100644
--- a/include/uapi/linux/bcache.h
+++ b/include/uapi/linux/bcache.h
@@ -144,14 +144,14 @@ static inline struct bkey
*bkey_idx(const struct bkey *k, unsigned nr_keys)
#define BCACHE_SB_VERSION_BDEV_WITH_OFFSET 4
#define BCACHE_SB_MAX_VERSION 4
-#define SB_SECTOR 8
+#define SB_SECTOR 128
#define SB_SIZE 4096
#define SB_LABEL_SIZE 32
#define SB_JOURNAL_BUCKETS 256U
/* SB_JOURNAL_BUCKETS must be divisible by BITS_PER_LONG */
#define MAX_CACHES_PER_SET 8
-#define BDEV_DATA_START_DEFAULT 16 /* sectors */
+#define BDEV_DATA_START_DEFAULT 256 /* sectors */
struct cache_sb {
__u64 csum;
The second arg of __bread(bdev, 16, SB_SIZE) has unit of block size
and it need be relocated too.
To suitable this change, bcache-tools need be fixed up too.
As for btree_node_size issues about page size, expecting somebody to
commit a patch.
Kent, maybe you could use qemu to simulate ARM64 arch and there is
always ubuntu image for ARM64 on the internet.
2016-06-02 7:16 GMT+08:00 Kent Overstreet <kent.overstreet@xxxxxxxxx>:
> On Wed, Jun 01, 2016 at 11:05:20AM -0700, Eric Wheeler wrote:
>> On Wed, 1 Jun 2016, Zhengyuan Liu wrote:
>>
>> > Hi, I have created a mapped block device (bcach0) using make-bcache on
>> > ARM64 server which has kernel enable 64K page size. However, the
>> > bcach0 disappeared after the server reboot and there is no or dirty
>> > metadata on super block of both cache device and back device . The
>> > output of command bcache-super-show was as bellow showed:
>> > [root@master Linux-4.4-LTS-storage]# bcache-super-show /dev/sdb
>> > sb.magic bad magic
>> > Invalid superblock (bad magic)
>> > /dev/sdb was the backing device and cache device got bad magic too.
>> >
>> > I tried to traced the written process of super block in bcache source
>> > code and found that is the issue of PAGE_SIZE. It seems that the
>> > bcache was designed only considering for 4K PAGE_SIZE and it works
>> > right only on 4K PAGE_SIZE exactly. To make bcache work correctly on
>> > 64K PAGE_SIZE, I committed a patch as bellow showd:
>> > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> > index 330cd6e..ef567cd 100644
>> > --- a/drivers/md/bcache/super.c
>> > +++ b/drivers/md/bcache/super.c
>> > @@ -224,6 +224,12 @@ static void __write_super(struct cache_sb
>> > *sb, struct bio *bio
>> > bio->bi_iter.bi_size = SB_SIZE;
>> > bch_bio_map(bio, NULL);
>> >
>> > +#ifdef CONFIG_ARM64_64K_PAGES
>> > + out = (struct cache_sb *)((char *)out + (SB_SECTOR<<9));
>> > + pr_debug("sb_page_adress %x, sb_address %x,page_size
>> > %d\n",page_address(bio
>> > + bio->bi_io_vec[0].bv_offset = (SB_SECTOR<<9);
>> > +#endif
>> >
>> > out->offset = cpu_to_le64(sb->offset);
>> > out->version = cpu_to_le64(sb->version);
>> >
>> > Does it not recommend to use bcache on 64K PAGE_SIZE? or it only
>> > considers for 4K PAGE_SIZE for bcache currently?
>> > Maybe it is more suitable for me to redefine some macro such as
>> > SB_SECTOR, BDEV_DATA_START_DEFAULT to make bcache work correctly on
>> > both 64K PAGE_SIZE and 4K PAGE_SIZE.
>>
>> I think a patch to support arbitrary page size would be great. Can
>> you write the macros in terms of PAGE_SIZE or PAGE_SHIFT?
>
> It shouldn't be referencing PAGE_SIZE at all - creating a new macro
> (BCH_SB_SIZE, perhaps) is the correct approach.
>
> The code that allocates the buffer for the superblock will have to be fixed
> too - right now it's probably using __get_free_page(), it should probably just
> be switched to kmalloc().
>
>> (Out of curiosity, what ARM64 hardware are you using?)
>>
>> Kent, this may affect bcachefs too. Can you think of any other places
>> that might have PAGE_SIZE!=4k issues?
>
> Oh, there's probably a couple. There's probably some stuff that'll break if
> btree_node_size is smaller than PAGE_SIZE, too...
>
> If it turns out to be too much for Zhengyuan, I can probably fix upstream too
> (but I don't have any hardware to test with).
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