Re: SSD "trim" support

[Simon Burge <simonb%NetBSD.org@localhost>]

Matthias Drochner wrote:

> Here is a prototype implementation for TRIM (or DELETE or how you
> call it) support for ffs.
> It is inspired by the FreeBSD implementation as this is done
> asynchronously in ffs_blkfree(), before the blocks are actually
> marked free in the filesystem.
> Since ffs (at least NetBSD's) frees blocks in reverse order
> I thought it was a good idea to collapse adjacent blocks
> already at the ffs level where this a-priori knowledge is
> present. This is different from FreeBSD; whether this is worth
> the effort is subject to research.
> This implementation handled only a single block range
> per transaction. SSDs can handle at least 64 vectors with
> one command. Extending the code should be simple.
> 
> I've given this some testing on an Intel and a Kingston
> SSD. Anyone interested in reviewing this, or more tests
> and optimizations?

Good stuff!  I'd gotten as far as printing a boot message if a disk
supported TRIM or not, but no time to go any further.

I've tried this on my 64GB OCZ Vertex 3, and it seems to have worked as
expected:

        # cp /test .
        # ls -l
        total 208
        -r--r--r--  1 simonb  wheel  104880 Apr 15  2008 test
        # rm test
        blkfree(1092,8192)
        enq old(1091,2048)
        defer(1092,8192)
        blkfree(1144,16384)
        enq old(1092,8192)
        defer(1144,16384)
        blkfree(1136,16384)
        defer(1136,32768)
        blkfree(1128,16384)
        trim(1091,2048):0
        defer(1128,49152)
        blkfree(1120,16384)
        trim(1092,8192):0
        defer(1120,65536)
        blkfree(1112,16384)
        defer(1112,81920)
        blkfree(1104,16384)
        defer(1104,98304)
        #

I did need to adjust the TRIMDEBUG printfs to use "PRId64" instead of
"lld" to get it to compile on my amd64.

One comment - the use of the name "TRIM" in the UFS layer could be a
bit more generic.  This same VOP could be used for example to handle
freeing up blocks with a flash device backing a UFS filesystem.  Maybe
use something like DIOCFREEBLOCKS instead of DIOCTRIM?

Cheers,
Simon.