Re: Frontswap [PATCH 0/4] (was Transcendent Memory): overview

[Pavel Machek <pavel@ucw.cz>]

> So there are two users of frontswap for which the synchronous
> interface makes sense.  I believe there may be more in the
> future and you disagree but, as Jeremy said, "a general Linux
> principle is not to overdesign interfaces for hypothetical users,
> only for real needs."  We have demonstrated there is a need
> with at least two users so the debate is only whether the
> number of users is two or more than two.
> 
> Frontswap is a very non-invasive patch and is very cleanly
> layered so that if it is not in the presence of either of 
> the intended "users", it can be turned off in many different
> ways with zero overhead (CONFIG'ed off) or extremely small overhead
> (frontswap_ops is never set; or frontswap_ops is set but the
> underlying hypervisor doesn't support it so frontswap_poolid
> never gets set).

Yet there are less invasive solutions available, like 'add trim
operation to swap_ops'.

So what needs to be said here is 'frontswap is XX times faster than
swap_ops based solution on workload YY'.
								       Pavel

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