<quote name="John McCabe-Dansted" date="Thu, 23 Dec 2010 at 15:50 +0800"> > On Thu, Dec 23, 2010 at 2:52 AM, Von Fugal <[email protected]> wrote: > > It really should sit as an in-between swap and memory place. Recently > > "swapped" pages should go straight to compcache, evicting pages if > > necessary *from* compcache to disk. That would be ideal. I don't know if > > the kernel devs would ever want to futz with the kernel that much, > > though. > > Compcache is a module that can be compiled by itself, so it doesn't > really need to be accepted by the Kernel devs. The real issue is > whether anyone (e.g the author of compcache) will find time to do > this.
What I was referring to was that it seems there might need to be additional kernel functionality to achieve this in-between not quite swap not quite ram place to put the compcache. I suppose you could code compcache to keep a certain margin open by itself initiating evictions when the threshold is passed. I wonder though how it would convince the kernel to store the evicted page into disk cache instead of itself(compcache) to actually keep that space available for new swaps. It seems though with any tiered cache system, the kernel should be actively moving less used pages down the hierarchy to put recently used pages in the higher priority caches anyway... The existence of prioritized caches would seem to imply that, though if the compcache "fills up" and becomes unavailable to new recent swaps, that would imply the opposite. > > I wonder why nobody has done compression on regular swap yet. I mean, > > the HUGE downside of swap is disk time, compressing the data on the disk > > would at least marginally speed up access time to that swapped data. > > I am guessing that the benefit is considered to be so small as to be > irrelevant: > > Seek time: ~10ms > Time to read 4K: ~0.05ms > Time to read 1K: ~0.01ms Yeah, I thought it might be something like this. I didn't think it through thoroughly. In my defense I *did* say "marginally" to mitigate such an oversight. ;) -- Von Fugal
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