Re: [f2fs-dev] [PATCH] f2fs: fix double count on issued discard commands

[Daeho Jeong <daeho.jeong@samsung.com>]

> Actually, we didn't change priority of discard command, so that it is still
> synchronous IO for I/O scheduler, hence I/O interference will still exist if we
> try to issue discard without IO aware ability.
 
> Of course we can change the priority of discard command to lower, but potential
> issue is that with ROW I/O scheduler in kernel or FTL, async I/O will handle
> very slowly in heavy load scenario, if we are going to trigger sync write IO in
> place in where we're doing async discard, we will face long latency.
 
> Still I think it is worth to build the ability to issue async discard as a part
> of discard policy and later we can adjust policy based on different scenario.
 
> Thanks,

Oh, I see.

f2fs is sending discard requests as "sync" requests, I didn't know that.
Right, I just though in case of CFQ I/O scheduler, but f2fs has to consider the other
schedulers, but CFQ.

Thanks, :)