On Fri, Nov 22, 2019 at 4:38 PM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > On Fri, Nov 22, 2019 at 10:18:38AM +1100, Dave Chinner wrote: > > On Thu, Nov 21, 2019 at 10:44:44PM +0100, Pavel Reichl wrote: > > > Signed-off-by: Pavel Reichl <preichl@xxxxxxxxxx> > > > --- > > > > This is mixing an explanation about why the change is being made > > and what was considered when making decisions about the change. > > > > e.g. my first questions on looking at the patch were: > > > > - why do we need to break up the discards into 2GB chunks? > > - why 2GB? > > Yeah, I'm wondering that too. OK, thank you both for the question - simple answer is that I took what is used in e2fsprogs as default and I expected a discussion about proper value during review process :-) > > > - why not use libblkid to query the maximum discard size > > and use that as the step size instead? > > FWIW my SATA SSDs the discard-max is 2G whereas on the NVME it's 2T. I > guess firmwares have gotten 1000x better in the past few years, possibly > because of the hundred or so 10x programmers that they've all been hiring. > > > - is there any performance impact from breaking up large > > discards that might be optimised by the kernel into many > > overlapping async operations into small, synchronous > > discards? > > Also: > What is the end goal that you have in mind? Is the progress reporting > the ultimate goal? Or is it to break up the BLKDISCARD calls so that > someone can ^C a mkfs operation and not have it just sit there > continuing to run? The goal is mainly the progress reporting but the possibility to do ^C is also convenient. It seems that some users are not happy about the BLKDISCARD taking too long and at the same time not being informed about that - so they think that the command actually hung. > > --D > > > i.e. the reviewer can read what the patch does, but that deosn't > > explain why the patch does this. Hence it's a good idea to explain > > the problem being solved or the feature requirements that have lead > > to the changes in the patch.... > > > > Cheers, > > > > Dave. > > -- > > Dave Chinner > > david@xxxxxxxxxxxxx >
