Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed)

[Mark Lord <liml@rtr.ca>]

John Robinson wrote:
..
> I'm slightly out of my depth here, but: if a single TRIM is issued, 
> which apparently returns quickly, can one then revert to issuing 
> ordinary commands like reads and writes and have them complete as 
> quickly as they normally do, or does any following command have to wait 
> until the trim completes? This could be useful if it turned out we won't 
> stall these devices as long as we don't issue more than one TRIM every 
> few seconds; we could keep a TRIM coalesce queue down to being (say) 5 
> seconds long (or at least, a configurable small number of seconds).
..

I have not attempted to instrument that, but I suspect that any
command after the TRIM has to wait.  Don't know for sure until
somebody measures it though.

One thing I do know, is that Matthew's first cut of TRIM support
means it takes half an hour to do "rm -r" on a kernel source tree.

-ml

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