Messages in this thread | | | From | "Duraid Madina" <> | Subject | VM: Where do we stand? | Date | Wed, 23 Jan 2002 20:32:03 +1100 |
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I'm sure at least some of you will immediately recognize these words:
> >Swap allocation is terrible. Linux uses a linear array which it scans >looking for a free swap block. It does a relatively simple swap >cluster cache, but eats the full linear scan if that fails which can be >terribly nasty. The swap clustering algorithm is a piece of crap, >too -- once swap becomes fragmented, the linux swapper falls on its face. > >It does read-ahead based on the swapblk which wouldn't be bad if it >clustered writes by object or didn't have a fragmentation problem. >As it stands, their read clustering is useless. Swap deallocation is >fast since they are using a simple reference count array. > >File read-ahead is half-hazard at best. > >The paging queues ( determing the age of the page and whether to >free or clean it) need to be written... the algorithms being used >are terrible. > > * For the nominal page scan, it is using a one-hand clock algorithm. > All I can say is: Oh my god! Are they nuts? That was abandoned > a decade ago. The priority mechanism they've implemented is nearly > useless. > > * To locate pages to swap out, it takes a pass through the task list. > Ostensibly it locates the task with the largest RSS to then try to > swap pages out from rather then select pages that are not in use. > From my read of the code, it also botches this badly. > >Linux does not appear to do any page coloring whatsoever, but it would >not be hard to add it in. >
Where does Linux stand, three years on? An O(1) scheduler is nice, but I tell you what'd be even nicer...
coming out for some food, (it's dark out) Duraid
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