File compression control, again.

File compression control, again.

[Artem]

Hi!

So, it makes sense to keep the compression on by default
and with LZO many people are going there.

But, I want to create a database on a compressed btrfs filesystem
which is seek-heavy rather than throughput-heavy
and I really want to turn the compression off just for that database
(smaller I/O reads, more precise cache usage).

Maintenance nightmare that Miguel mentioned
( http://thread.gmane.org/gmane.comp.file-systems.btrfs/1665/focus=1669 )
isn't really a problem as I'm going to automatically set the flags
from the program, just before opening the database.

Looking at "fs/btrfs/ioctl.h" I don't see any way to to this.
Subvolume compression control isn't working either from what I heard
(cf. https://bbs.archlinux.org/viewtopic.php?id=126635
     http://thread.gmane.org/gmane.comp.file-systems.btrfs/6237/ ).

Am I right that fine-grained compression control is no longer supported by btrfs?
If so, I would like to vote for it to be added.

Re: File compression control, again.

[Li Zefan]

01:17, Artem worte:
> Hi!
> 
> So, it makes sense to keep the compression on by default
> and with LZO many people are going there.
> 
> But, I want to create a database on a compressed btrfs filesystem
> which is seek-heavy rather than throughput-heavy
> and I really want to turn the compression off just for that database
> (smaller I/O reads, more precise cache usage).
> 
> Maintenance nightmare that Miguel mentioned
> ( http://thread.gmane.org/gmane.comp.file-systems.btrfs/1665/focus=1669 )
> isn't really a problem as I'm going to automatically set the flags
> from the program, just before opening the database.
> 
> Looking at "fs/btrfs/ioctl.h" I don't see any way to to this.
> Subvolume compression control isn't working either from what I heard
> (cf. https://bbs.archlinux.org/viewtopic.php?id=126635
>      http://thread.gmane.org/gmane.comp.file-systems.btrfs/6237/ ).
> 
> Am I right that fine-grained compression control is no longer supported by btrfs?
> If so, I would like to vote for it to be added.
> 

See this "Per file/directory controls for COW and compression":

	http://marc.info/?l=linux-btrfs&m=130078867208491&w=2

And the user tool patch (which got no reply):

	http://marc.info/?l=linux-btrfs&m=130311215721242&w=2

So you can create a directory, and set the no-compress flag for it, and
then any file created in that dir will inherit the flag.

Re: File compression control, again.

[Artem]

Li Zefan <lizf <at> cn.fujitsu.com> writes:
> See this "Per file/directory controls for COW and compression":
> 
> 	http://marc.info/?l=linux-btrfs&m=130078867208491&w=2
> 
> And the user tool patch (which got no reply):
> 
> 	http://marc.info/?l=linux-btrfs&m=130311215721242&w=2
> 
> So you can create a directory, and set the no-compress flag for it, and
> then any file created in that dir will inherit the flag.

Thanks, Li, but how do I set the no-compress flag?
The patched chattr you mention can only set the FS_COMPR_FL.
The 'C' argument is now used for FS_NOCOW_FL.

Could we use another flag for copy-on-write control in chattr?

Re: File compression control, again.

[Artem]

Li Zefan <lizf <at> cn.fujitsu.com> writes:
> See this "Per file/directory controls for COW and compression":
> 
> 	http://marc.info/?l=linux-btrfs&m=130078867208491&w=2

Thanks again!
I wrote a program to see if ioctl compression control works
( https://gist.github.com/1248085 )
and it does!  : )

Re: File compression control, again.

[David Sterba]

On Wed, Sep 28, 2011 at 02:50:13PM +0000, Artem wrote:
> Li Zefan <lizf <at> cn.fujitsu.com> writes:
> > See this "Per file/directory controls for COW and compression":
> > 
> > 	http://marc.info/?l=linux-btrfs&m=130078867208491&w=2
> 
> Thanks again!
> I wrote a program to see if ioctl compression control works
> ( https://gist.github.com/1248085 )

you have to call IOC_GETFLAGS first, then

flags |= FS_NOCOMP_FL;

27  int flags = compression ? FS_COMPR_FL : FS_NOCOMP_FL;
28  int ret = ioctl (fd, FS_IOC_SETFLAGS, &flags);

else all other flags will be dropped.


david