> 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.
Agreed, scanning for a swap block can take too much CPU
on large machines. We've seen this happen ...
> >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.
Swap readahead improvements very much welcome.
> >File read-ahead is half-hazard at best.
How so? File read-ahead seems to work pretty well.
> >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.
Fixed in -rmap, http://surriel.com/patches/
> >Linux does not appear to do any page coloring whatsoever, but it would
> >not be hard to add it in.
Not sure how page colouring would interact with the buddy
allocator, though ;)
> Where does Linux stand, three years on? An O(1) scheduler is
> nice, but I tell you what'd be even nicer...
I'm working on some of the above issues for the -rmap VM;
if there's something else which really bugs you, I accept
patches ;)
cheers,
Rik
--
"Linux holds advantages over the single-vendor commercial OS"
-- Microsoft's "Competing with Linux" document
http://www.surriel.com/ http://distro.conectiva.com/
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