On Fr, 20.12.19 18:11, Louis Lagendijk (louis(a)fazant.net) wrote:
On Fri, 2019-12-20 at 17:46 +0100, Lennart Poettering wrote:
>
> Or let me ask this differently: the "discard" mount option of various
> kernel file systems, what does it differently than what this new
> fedora feature is supposed to do?
>
fstrim does the discard once a week (or whenever it it triggered),
discard as a mount option does trigger discard when a block is freed.
Depending on the drive it may actually slow down IO as the SSD will
need more time to finish the IO. Doing an fstrim leaves the processing
to the SDD. That was the argument years ago. I don't know if this is
Hmm? if the if the fs enqeues the trimming or userspace does, it's
always the SSD that executes it...
still true for modern SSD's. For older SSDs fstrim would stil be
the
safer option. And automatic trimming is long overdue in my opinion.
So if trimming is slow, that's still no reason to let userspace pick a
time for it. Sounds like the kernel fs should have discard=lazy or
discard=5min or so. Which would enqueue a trim run automatically after
the last IO after some delay.
Still not grokking why to do this in userspace.
--
Lennart Poettering, Berlin