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?
(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?
-Eric
--
Eric Wheeler
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