Re: [PATCH 01/15] btrfs: Honour FITRIM range constraints during free space trim

David Sterba
2019-01-31T15:48:57Z

On Thu, Jan 31, 2019 at 05:35:10PM +0200, Nikolay Borisov wrote:
> On 31.01.19 г. 17:21 ч., David Sterba wrote:
> > On Wed, Jan 30, 2019 at 04:50:48PM +0200, Nikolay Borisov wrote:
> >> Up until know trimming the freespace was done irrespective of what the
> >> arguments of the FITRIM ioctl were. For example fstrim's -o/-l arguments
> >> will be entirely ignored. Fix it by correctly handling those paramter.
> >> This requires breaking if the found freespace extent is after the end
> >> of the passed range as well as completing trim after trimming
> >> fstrim_range::len bytes.
> >
> > How does this work with with multipe-device filesystems? The fstrim
> > range would apply to all of them. Which does make some sense, though
> > might be unexpected as this does not happen for other filesystems.
>
> Well FITRIM doesn't have support for multiple device so it's to the
> discretion of the fs how exactly this is implemented. And this is indeed
> the way things work currently.
>
> > The FITRIM range is in the physical coordinates, so eg. the taking the
> > maximum size of all devices and iterating over that by 1GiB steps would
> > go though the whole filesystem. Something to put to the changelog and
> > documentation.
>
> I don't follow, trimming would just trim the physical range as passed by
> fstrim -o/-l options. That 1gb value is not hardcoded anywhere. If
> someone wants to trim all of the freespace (which is what the majority
> of the user do) then they can run FITRIM with 0 for offset and -1 for
> length.

Yeah but I wanted to give an example of usecase when the range is not
0/-1 and how this is could to be used.