Hi! On 20/02/06, Hannah Schroeter <[EMAIL PROTECTED]> wrote: > Hello! > > On Sat, Feb 18, 2006 at 03:40:48PM +0000, Constantine A. Murenin wrote: > >I have a box with 512MB of RAM, which is running a snapshot from 2006-02-13. > > >The box does not get used much, so most of the RAM stays still, i.e. > >not used by the userland. > > >I am now quite surprised why OpenBSD does not use all of this RAM for > >disc cache etc. > > Because nobody has submitted code that actually gets it right. There > was code for unified VM/buffer cache in the tree once, but got reverted > a few weeks later when it showed itself that there were significant > problems with it. > > Just one "effect" you have to care for, on Linux (which *has* a unified > VM/buffer cache system) we mkdir many directories (e.g. hashed buckets > like squid uses them, just a few more, 256 * 256, to be precise). It was > quite long (at least into the Linux 2.4 series) that that worked like > this: mkdir completed quite fast until the memory was filled with dirty > blocks, then the box *hung* completely until all the dirty blocks were > actually written to disk. This isn't acceptable. And it's not acceptable > for something like grep foo (a list of names of long files) pages out > every program. > > Just two things where it shows how difficult it can be to get things > right. It's much easier to get it right as it is in OpenBSD.
Yes, there is always some compromise. But in this specific case we have much less than even a fifth of memory actually being used for programmes and kernel etc. Some of the rest is used for cache, but it still stops at around 3/4 or even 4/5 of the memory being wasted for nothing. We are not dealing here with a case of someone wanting to use the remaining 64MB for disc cache on a 2GB server (assuming the rest of memory being already utilised for cache): -- this is a case of a 512MB machine behaving as if it was a 128MB one, not using the extra 3/4 of available memory. I assume that even if I put the extra 1G in, the proportion of wasted memory will only increase. And 512MB, I must add, is the de facto minimum today for any machine, making this even lack of tune-up even more unacceptable. Cheers, Constantine.
