Re: mmaping on plan9? (was Re: [9fans] venti /plan9port mmapped

["Danny Wilkins via 9fans" <9fans@9fans.net>]

On Fri, Feb 13, 2026 at 09:21:21AM -0800, ron minnich wrote:
> As for needing or not needing mmap, you need to consider how you support
> efficient access for files 100x or greater in size than physical memory.
> I'm not sure what your plan is there. It's a real world problem however.
> Or, further, files that contain data which are pointers.
> 
Hi Ron,
Probably showing my ignorance but out of curiosity, what *is* the difference
here? I can certainly see the open/read method requiring some bikeshedding on
the buffer size, but you could jump to a pointer with seek. Is there some
nasty behavior on how much memory an open file will consume as you jump around
in it beyond the fixed info maintained for the fd and the buffer allocated
by the caller?
I want to say I've been in that situation, though in a weird way :)
If I recall correctly, I messed with some files in the GB size range on a box
with 16 MB of memory last year, but that was pretty much just dd so it may have
been an optimal usage pattern (linear read from start to end, blocksize buffer.)

Thanks,
Danny


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