Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Jan 14, 2014 at 11:57 AM, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
>> No, I do ... you mean the order of write out, if we have to do it, is
>> important. In the rest of the kernel, we do this with barriers which
>> causes ordered grouping of I/O chunks. If we could force a similar
>> ordering in the writeout code, is that enough?
> Probably not. There are a whole raft of problems here. For that to
> be any of any use, we'd have to move to mmap()ing each buffer instead
> of read()ing them in, and apparently mmap() doesn't scale well to
> millions of mappings.
We would presumably mmap whole files, not individual pages (at least
on 64-bit machines; else address space size is going to be a problem).
However, without a fix for the critical-section/atomic-update problem,
the idea's still going nowhere.
> This would be pretty similar to copy-on-write, except without the
> copying. It would just be forget-from-the-buffer-pool-on-write.
That might possibly work.
regards, tom lane
