Re: Getting TRIM working

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Mar 09, 2009 at 02:04:55PM +0000, James Bottomley wrote:
> > Disadvantages:
> >  - UNMAP gets less testing
> 
> Also disadvantages: UNMAP will not work unless trim is pulled back out
> of libata again ... which makes this look a bit like a temporary hack.

Huh?  sd.c will continue to have sd_discard_fn() which will work fine
for UNMAP.  This will give us a different path for ATA discs and SCSI
discs, as far as discard functions go.

> As I've said before, I don't like the bio based approach.  I think you
> leak a page on every trim command doing it (why?  because the kernel
> mapped bios have special bio->end_io routines to collect and free the
> pages, you have no such routine).

I added that in an earlier patch:

http://git.kernel.org/?p=linux/kernel/git/willy/ssd.git;a=commitdiff;h=f6ebf54cb8045a0cab19d73e26a07945c29d1394;hp=1223b373ae0283221b46e70955eb825679c5a6cb

I'm all in favour of a less messy approach than using bios directly, if
there is one.  I don't see what it might look like yet.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."