Re: Linux max on shared buffers?

Curt Sampson wrote:
>
> On Fri, 19 Jul 2002, Tom Lane wrote:
>
> > Just to throw some additional wrenches into the gears: some platforms
> > (eg HPPA) have strong restrictions on where you can mmap stuff.
> > I quote some interesting material from the HPUX mmap(2) man page below.
> > Possibly these restrictions could be worked around, but it looks
> > painful.
>
> Very painful indeed. Probably it would be much easier to build a little
> mmap-type interface on top of the current system and use that instead of
> mmap on such a system. I wonder how many other systems are this screwed up?

I have some more wrinkles to iron out as well. We can hold blocks of
hundreds of different files in our buffer cache without the need to keep
an open file descriptor (there is a reason for our VFD system). Access
to those blocks requires a spinlock and hash lookup in the buffer cache.
In a complicated schema where you cannot keep all files open anymore,
access to your kernel buffered blocks requires open(), mmap(), munmap()
and close() then? Four system calls to get access to a cached block
where we get away with a TAS today?


Jan

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