Messages in this thread | | | Date | Mon, 10 Aug 2009 12:47:24 -1000 | From | Zachary Amsden <> | Subject | Re: [PATCH] Allow userspace block device implementation |
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Pavel Machek wrote: > Hi!
Hey!
> And yes, I believe that's show stopper. OTOH if you _can_ solve > that... then you have some rather significant advantage over nbd. > > (But guaranteeing progress for dirty writeout will be tricky even with > mlocked userland, AFAICT...)
Actually, impossible, even with mlocked userland (*) which is what led me to abandon going any further with it. The problem is, to commit any data, one must make a system call, thus consuming more resources. It's merely a toy, nothing more. Sometimes it might be a useful toy, as nbd, but nbd, being in kernel, has at least a better chance of solving the swap problem.
(*) strictly speaking, it is possible to guarantee progress of the device for read/write only to a finite region of mlocked memory and an infinite region (limited only by size of off_t) of read-only data computable with finite mlocked space. Obviously, neither of these (swap-to-ram), and (swap-over-ro-media) are actually useful for swap.
Zach
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