CFT: TRIM Consolodation on UFS/FFS filesystems

[Kirk McKusick]

> Date: Wed, 5 Sep 2018 17:12:17 -0700
> From: bob prohaska <fbsd at www.zefox.net>
> To: Kirk McKusick <mckusick at mckusick.com>
> Cc: Mark Millard <marklmi at yahoo.com>,
>         FreeBSD Filesystems <freebsd-fs at FreeBSD.org>,
>         bob prohaska <fbsd at www.zefox.net>
> Subject: Re: CFT: TRIM Consolodation on UFS/FFS filesystems
> 
> Just for fun I ran a (somewhat absurd) -j4 buildworld on RPI3 using
> 6 GB of swap, three on USB and three on microSD, just to see if
> anything interesting (bad) happened.  The process took about 24
> hours, and  the oversuppy of swap didn't cause any obvious problems.
> Next I turned on TRIM and re-ran the buildworld script.
> 
> There were no obvious problems, but the process took about an extra
> hour.  Since /var, /tmp and /usr were all on USB there was no hope
> TRIM could be any help on the busy filesystems. TRIM was enabled
> on microSD, but it had little to do. There does seem to be a modest
> penalty for using TRIM when it can't help much.
> 
> Is there any hope of implementing something like TRIM for USB on
> the Pi?  It appears that congestion on USB is a serious bottlneck
> from time to time just for traffic with /tmp and /usr. Adding swap
> to the mix makes it worse.
> 
> Log files are at
> http://www.zefox.net/~fbsd/rpi3/swaptests/r338342/3gbsd_3gbusb/
> in case they're of interest.
> 
> Thanks for reading!
> 
> bob prohaska

Thanks for the additional information. My guess is that there will
not be any move to pass TRIM through to USB devices as there is no
standard way to do it, and in cases where it has been sort of hacked
in, there has been no perceived benefit and in some cases severe
performance penalties.

	Kirk McKusick