Re: how to free a used ag?

[Markus Lidel <Markus.Lidel@xxxxxxxxxxxxxxxxx>]

Hello,

Steve Lord wrote:
> Markus Lidel wrote:
> > could someone help me with freeing a used ag?
> > I want to do it inside the kernel and while the fs is mounted. I've 
> > already looked at the code, and it looks to me that freeing the agi of 
> > an ag is the easier part, so i want to start with it. I thought i 
> > could look at each inode of the agi i want to free, but i think i must 
> > iterate over each inode when freeing the used blocks anyway. So i 
> > iterate over each inode (starting with the root inode) and move the 
> > inode to a new one if it is inside the ag which should be freed. The 
> > second step is to look at the inode itself. If the data block is 
> > inside the ag it could be moved outside the ag too.
> > If i missed something until here, please let me know:-)
> Make sure you traverse all the inodes - there will probably be inodes
> in different allocation groups which have extents in the targeted ag.
> When you move an inode you need to fix up all the directories which
> point at it. It is going to get a new inode number, so you need to walk
> the directory tree looking for that inode number and replacing it. 
> Remember,
> hard links mean an inode number could show up more than once.

Thanks you very much for the advice... But do you think it's better to 
work on the on-disk structure, or do you think it's better to work with 
the in-core inodes?

> > 2. how could i easily copy the inode to a free space outside the current
> >    agi (i thought of setting pag.pagf_freeblks, pag.pagf_flcount,
> >    pag.pagf_longest to 0).
> You need a mechanism to drain all the transactions in progress (look at
> the freeze code), then flag the per ag structures in some way so that
> the allocator will not use them. A temporary in memory flag in the
> per ag headers is probably best. Then start up transactions again.

Hmmm, if i work on the in-core structures, do i have to care about 
transactions too?

> > 3. have i missed something or is there a better way to do it?
> You might want to try this from user space with some kernel assist rather
> than doing it all in the kernel. The bulkstat and swap extent calls provide
> the meat of the tools you need to do this.
> Of course, you need sufficient free space to recreate everything
> outside those

Okay...

> allocation groups. If you are removing some space from the filesystem, the
> allocator probably needs to be told that the filesystem is smaller than it
> actually is, or you may get into states where one part of the allocator 
> thinks
> there is room, but it cannot actually find the space.

This is the only thing which is working right now :-)


Thank you very much for your help!



Best regards,


Markus Lidel
------------------------------------------
Markus Lidel (Senior IT Consultant)

Shadow Connect GmbH
Carl-Reisch-Weg 12
D-86381 Krumbach
Germany

Phone:  +49 82 82/99 51-0
Fax:    +49 82 82/99 51-11

E-Mail: Markus.Lidel@xxxxxxxxxxxxxxxxx
URL:    http://www.shadowconnect.com

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