[dm-devel] super-block written got dislocation while 64K PAGE_SIZE enable.

[Zhengyuan Liu]

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 at gmail.com>:

> 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 at 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).
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/dm-devel/attachments/20160602/3447adca/attachment.htm>