On Mon, Jul 27, 2020 at 6:18 PM Xiao Ni [off-list ref] wrote:

On 07/28/2020 01:33 AM, Song Liu wrote:

quoted

On Tue, Jun 30, 2020 at 12:55 AM Xiao Ni [off-list ref] wrote:

quoted

One super1.0 raid array wants to grow size, it needs to check the device max usable
size. If the requested size is bigger than max usable size, it will return an error.

Now it uses rdev->sectors for max usable size. If one disk is 500G and the raid device
only uses the 100GB of this disk. rdev->sectors can't tell the real max usable size.
The max usable size should be dev_size-(superblock_size+bitmap_size+badblock_size).

Signed-off-by: Xiao Ni <redacted>

Thanks for the fix!

quoted

---
  drivers/md/md.c | 26 +++++++++++++++++++++++---
  1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f567f53..d2c5984 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -2183,10 +2183,30 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
                 return 0;
         } else {
                 /* minor version 0; superblock after data */
-               sector_t sb_start;
-               sb_start = (i_size_read(rdev->bdev->bd_inode) >> 9) - 8*2;
+               sector_t sb_start, bm_space;
+               sector_t dev_size = i_size_read(rdev->bdev->bd_inode) >> 9;
+
+               /* 8K is for superblock */
+               sb_start = dev_size - 8*2;
                 sb_start &= ~(sector_t)(4*2 - 1);
-               max_sectors = rdev->sectors + sb_start - rdev->sb_start;
+
+               /* if the device is bigger than 8Gig, save 64k for bitmap usage,
+                * if bigger than 200Gig, save 128k
+                */
+               if (dev_size < 64*2)
+                       bm_space = 0;
+               else if (dev_size - 64*2 >= 200*1024*1024*2)
+                       bm_space = 128*2;
+               else if (dev_size - 4*2 > 8*1024*1024*2)
+                       bm_space = 64*2;
+               else
+                       bm_space = 4*2;

Could you explain the handling of bitmap space?

Hi Song

This calculation of bitmap is decided by mdadm. In mdadm super1.c
choose_bm_space function,
it uses this way to calculate bitmap space. Do I need to add comments
here to describe this?
Something like "mdadm function choose_bm_space decides the bitmap space"?

Thanks for the explanation.

I merged the two patches, made some changes, and applied it to md-next. Please
let me know whether it looks good.

Song