Rainer Toebbicke wrote:
Does the disk cache take advantage of linux's disk cache? I'm thinking
that is a freebie if we use tmpfs or some other linux-provided fs-backed
cache.
Yes, it does, it just reads cache files like any vanilla user space
process.
This has two consequences:
1. tmpfs on linux just works fine, if you have a (small) patch that
glues the inode-centric file opens to the dentry-centric tmpfs files. I
suspect the work done to make OSX happy obsoletes this patch if it can
be made to work under Linux.
It looks like it should be easy. It was for Solaris 10 so it can run
on tmpfs or ZFS. See http://rt.central.org/rt/Ticket/Display.html?id=123677
all the code change is in osi_file.c, and the param.<sysname>.h files.
Actually, since tmpfs's disk backing can span disks this would be an
attractive option to speed up the cache. But we never deployed that
patch it on a big scale as it required resizing existing machines (more
swap, no AFS cache).
The downside is of course that you loose your cache upon reboot. I guess
disconnected-AFS users might consider that serious.
2. AFS files end up twice in memory, once in the mapping of the AFS file
itself and then in the mapping of the cache chunk. We've addressed this
by short-circuiting the VM layer for the AFS file, a relatively
straightforward mod, but which gets messy as you still need that layer
for everything that is memory-mapped, such as executables.
--
Douglas E. Engert <[EMAIL PROTECTED]>
Argonne National Laboratory
9700 South Cass Avenue
Argonne, Illinois 60439
(630) 252-5444
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