First, Thanks for your replies. Let me followup with a few more
questions and notes.
>From: "Theodore Y. Ts'o" <tytso@MIT.EDU>
>
> [5] All of FreeBSD/NetBSD/Linux write out only the dirty pages to
> swap space, choosing to read in the read-only (code) pages
> from the file system.
>
>Is this true of FreeBSD/NetBSD? It wasn't true of BSD 4.3; I don't
>know about BSD 4.4
I think so. The 4.4BSD book itself talks about writing dirty pages
to swap when page frames are in short supply - but this discussion
in the book is disjoint from the discussion of swapping (complete)
processes to disk. I am not clear on how complete swapping and
writing pages to swap as part of page-replacement interact.
I'll take this up with some FreeBSD folk and see what they have to
say.
a)
For linux, would I be correct in saying that swapping is handled as
part of page-replacemnt and there is no module which hunts for
candidate processes whose pages can be marked for swapping.
b)
Is the page replacemnt in Linux Global-LRU? 4.4BSD had global-LRU
and I think that policy has been retained in the *BSDs.
Alan Cox (on FS buffer cache being implemented on top of VM)
> A separate dynamically varying buffer cache is used to hold
> metadata. <snip>
> So Linux and FreeBSD are close together on this one.
Does FreeBSD use a dynamic buffer cache for the metadata too?
I missed a couple of questions in my last mail:
[7] In order to be able to run over different architectures, Linux
implements a 3-level page table. It then rolls the architecture
specific stuff into this 3-level organization. For example x86
has only 2-level page tables but these are appropriately munged
into the 3-level organization. My question is that, are there
any architectures out there for which this sort of transformation
won't work? i.e does the transformation take away enough from
the architectures strengths that other hacks are needed to be
able to get reasonable performance?
[8] Is there any project going on in the Linux community to support
page coloring? FreeBSD implements this but NetBSD doesn't.
Thanks much.
-dj
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