Re: [ANNOUNCE][PATCH 2.6] md: persistent (file-backed) bitmap and async writes

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Hi Neil,

Here's the next round of patches:

kernel patch against 2.6.7:
--------------------------
http://www.parisc-linux.org/~jejb/md_bitmap/md_bitmap_2_32_2_6_7.diff

mdadm patch against 1.6.0:
-------------------------
http://www.parisc-linux.org/~jejb/md_bitmap/md_bitmap_2_32_2_6_7.diff


Details below...


Neil Brown wrote:
On Tuesday June 8, paul.clements@xxxxxxxxxxxx wrote:

This looks a lot better.  There are a few little issues that I noticed
on a quick read through:
     - last_block_device should return "sector_t", not "unsigned
       long".  It would be worth checking for other placed that
       sector_t might be needed.

Fixed.

     - bitmap_checkpage still isn't quite safe.  If "hijacked" gets
       set while it is allocating a page (unlikely, but possible), it
       will exit with both highjacked set and an allocated page, which
       isn't right.

Fixed.

- The event comparison
+ sb->events_hi >= refsb->bitmap_events_hi &&
+ sb->events_lo >= refsb->bitmap_events_lo) {
in hot_add_disk is wrong.

This is still there, see my explanation in the previous email...

The changes to mdadm need a bit of work.
You have added "--persistent" and "--non-persistent" flags for
--create. This is wrong.
--create always uses persistent superblocks.
--build makes arrays without persistent superblocks.

OK, changed. The --build command now also accepts the --bitmap option.

I don't think I like --create-bitmap.  A bitmap file should always be
created in the context of a particular array (partly so that the size
and uuid can be set correctly).  I think I would like to bitmap to be
specified as a "--bitmap=filename" option to --create, --build, or
--grow.  I haven't thought this through in great detail yet, but that
is my leaning.

OK, --create-bitmap remains solely for the --build case, but is no longer needed for --create. The --create command now does all the array creation in userspace and simply Assembles the resulting collection of disks. It also initialises the bitmap correctly for use with the array (i.e., uuid and size match).


--examine-bitmap is a bit of a pain too.  I think I would like
--examine to figure out what it has been given to look at, and report
on whatever it finds.

This also remains as-is for now, pending your reply to my previous emails.


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