| From: | Greg Stark <stark(at)mit(dot)edu> |
|---|---|
| To: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
| Cc: | KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, Tatsuo Ishii <ishii(at)postgresql(dot)org>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Magnus Hagander <magnus(at)hagander(dot)net>, Josh Berkus <josh(at)agliodbs(dot)com>, Stefan Kaltenbrunner <stefan(at)kaltenbrunner(dot)cc>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Why we are going to have to go DirectIO |
| Date: | 2013-12-05 15:40:58 |
| Message-ID: | CAM-w4HM++8QgNjjRZLTCPSKHBF1+awKxGJAd3csKR4Mj-+1uiQ@mail.gmail.com |
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On Thu, Dec 5, 2013 at 2:54 PM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> That's a bad idea in the current state of affairs. MM files haven't
> been designed for that usage, and getting stable performance out of
> that will be way too difficult.
I'm talking about long-term goals here. Either of these two routes
would require whole new kernel interfaces to work effectively. Without
those new kernel interfaces our current approach is possibly the best
we can get.
I think the way to use mmap would be to mmap very large chunks,
possibly whole tables. We would need some way to control page flushes
that doesn't involve splitting mappings and can be efficiently
controlled without having the kernel storing arbitrarily large tags on
page tables or searching through all the page tables to mark pages
flushable.
--
greg
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