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

[tlaronde@kergis.com]

On Sun, Feb 15, 2026 at 09:24:32PM -0500, Alyssa M via 9fans wrote:
> I think the difficulty here is thinking about this as memory mapping. What I'm really doing is deferred I/O. By the time a read completes, the read has logically happened, it's just that not all of the data has been transferred yet.
> That happens later as the buffer is examined, and if pages of the buffer are not examined, it doesn't happen in those pages at all. 
> 

But isn't this what the buffer cache does? My concern with this scheme
is the sharing (concurrent accesses, even with only one rw and several
read-only: what are the read-only ones really reading and when): if
there is a kernel side resources server, only when the writing process
does "commit", the data is officially modified and with a central
server the information can be propagated. With a per process mapping,
on what criterium will the data be marked as "officially" modified
with the concurrent accesses having to be informed? If the process has
(as it should) to inform (to commit modified data) and don't see what
is different from the traditional scheme and I don't get what it
improves---my gut feeling is the reverse: it would be more tricky to
get it right and the complexity will certainly not improve the
performance.
-- 
        Thierry Laronde <tlaronde +AT+ kergis +dot+ com>
                     http://www.kergis.com/
                    http://kertex.kergis.com/
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