CFT: TRIM Consolodation on UFS/FFS filesystems

[Kirk McKusick]

> From: Mark Millard <marklmi at yahoo.com>
> Subject: Re: CFT: TRIM Consolodation on UFS/FFS filesystems
> Date: Wed, 5 Sep 2018 00:06:54 -0700
> Cc: bob prohaska <fbsd at www.zefox.net>,
>         FreeBSD Filesystems <freebsd-fs at FreeBSD.org>
> To: Kirk McKusick <mckusick at mckusick.com>
> 
> On 2018-Sep-4, at 10:20 PM, Kirk McKusick <mckusick at mckusick.com> wrote:
> 
>> Thanks for the report. Do you have a sense/measurement that the
>> build times better/same/worse than without the consolidation?
> 
> ...
> 
> But installworld is far more I/O bound and does take something
> like 11 or 12 minutes in this context. (installkernel is also
> more I/O bound but takes far less time.)
> 
> I have a record of an updating installworld for
> clang-cortexA53-installworld-poud already with consolidation
> turned on . . .
> 
> Start time: 2018-09-04:12:48:14
> End   time: 2018-09-04:12:59:54 (so 11 min 40 sec or so elapsed)
> typescript log size: 8698790
> 
> So after the poudriere/pkg activity I could repeat the
> "-j4 installworld distrib-dirs distribution DB_FROM_SRC=1
> DESTDIR=/usr/obj/DESTDIRs/clang-cortexA53-installworld-poud"
> with the new consolidation turned off. (That would leave
> active the mmc/sd code's consolidation that Ian L.
> referenced.)
> 
> I could also try yet again but with trim disabled for the file
> system, giving a 3rd contrasting case.
> 
> Would these comparisons help?
> 
> ===
> Mark Millard
> marklmi at yahoo.com
> ( dsl-only.net went
> away in early 2018-Mar)

The above three comparisons on the (relatively) I/O bound installworld
would be useful. Even if the TRIM consolidation does not help, it is
useful to know that it does not hurt. And running without TRIM would
also be a useful data point to measure the cost/savings of doing TRIM.

It is a bit tricky to just turn off TRIM and then measure it, because
in the immediate aftermath of its having been used, it will leave
behind a legacy of easier to use flash areas yet not have the cost
of keeping them cleaned up. So, it might initially look like enabling
TRIM is a bad idea. Thus you would have to run many installworlds
without TRIM enabled to see what the long-term result of not using
TRIM turns out to be.

	Kirk McKusick