Re: [PATCH] mm: don't discard unused swap slots by default

["Martin K. Petersen" <martin.petersen@oracle.com>]

>>>>> "Hugh" == Hugh Dickins <hugh.dickins@tiscali.co.uk> writes:

Hugh> You mentioned an "-o discard" mount option before: so I think what
Hugh> we ought to be doing is an option to swapon.  But you can imagine
Hugh> that I'd prefer to avoid that too, if we can work this out without
Hugh> it.

The main problem we have is that the devices currently supporting TRIM
are doing a piss poor job at it.

We have pretty good vendor guarantees that discards are going to be
essentially free on SCSI-class hardware.  But in the ATA space things
are currently being driven by early adopters / tweakers that care more
about benchmarketing and feature checklists.  Whether things actually
work as intended is mostly irrelevant.

I think we'll need to give things a little bit of time for decent ATA
TRIM implementations to materialize.  And then we can switch to an
"assume it works, blacklist bad eggs" approach.  Until then I think we
need to make discard an explicit opt-in feature.

-- 
Martin K. Petersen	Oracle Linux Engineering

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