From: Larry McVoy <lm@mcvoy.com>
To: Bakul Shah <bakul@iitbombay.org>
Cc: TUHS main list <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] FreeBSD behind the times? (was: Favorite unix design principles?)
Date: Fri, 5 Feb 2021 06:18:20 -0800 [thread overview]
Message-ID: <20210205141820.GO13701@mcvoy.com> (raw)
In-Reply-To: <26D923CF-5319-4207-BA28-6EFA0E3BB1F8@iitbombay.org>
On Thu, Feb 04, 2021 at 09:17:54PM -0800, Bakul Shah wrote:
> On Feb 4, 2021, at 4:33 PM, Larry McVoy <lm@mcvoy.com> wrote:
> >
> > Ignoring the page cache and make their own cache has big problems.
> > You can mmap() ZFS files and doing so means that when a page is referenced
> > it is copied from the ZFS cache to the page cache. That creates a
> > coherency problem, I can write via the mapping and I can write via
> > write(2) and now you have two copies of the data that don't match,
> > that's pretty much OS no-no #1.
>
> Write(2)ing to a mapped page sounds pretty dodgy. Likely to get you
> in trouble in any case. Similarly read(2)ing.
The entire point of the SunOS 4.0 VM system was that the page you
saw via mmap(2) is the exact same page you saw via read(2). It's
the page cache, it has page sized chunks of memory that cache
file,offset pairs.
There is one, and only one, copy of the truth. Doesn't matter how
you get at it, there is only one "it".
ZFS broke that contract and that was a step backwards in terms of
OS design.
next prev parent reply other threads:[~2021-02-05 14:19 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-25 11:10 [TUHS] Favorite unix design principles? Tyler Adams
2021-01-25 12:32 ` Steve Nickolas
2021-01-26 2:06 ` M Douglas McIlroy
2021-01-26 2:53 ` Steve Nickolas
2021-01-26 10:22 ` Tyler Adams
2021-01-26 12:26 ` John P. Linderman
2021-01-26 15:23 ` Clem Cole
2021-01-26 16:00 ` Niklas Karlsson
2021-01-26 16:13 ` Adam Thornton
[not found] ` <CAKH6PiXKjksEpQOMMMQTbcsMvX2thz3WzqjoRWJAsXnZ4Eq_iQ@mail.gmail.com>
2021-01-30 19:01 ` Tyler Adams
2021-01-30 19:50 ` Jon Steinhart
2021-01-30 20:06 ` Tyler Adams
2021-01-30 21:28 ` Clem Cole
2021-01-30 21:42 ` Dave Horsfall
2021-01-30 21:45 ` Tyler Adams
2021-01-30 22:31 ` Larry McVoy
2021-01-30 22:28 ` Larry McVoy
2021-01-30 23:11 ` [TUHS] FreeBSD behind the times? (was: Favorite unix design principles?) Greg 'groggy' Lehey
2021-01-30 23:17 ` Larry McVoy
2021-01-30 23:22 ` Warner Losh
2021-01-30 23:31 ` [TUHS] [SPAM] " Larry McVoy
2021-01-30 23:37 ` Jon Steinhart
2021-01-30 23:54 ` Larry McVoy
2021-01-31 12:23 ` [TUHS] [SPAM] Re: FreeBSD behind the times? Dermot Tynan
2021-01-31 0:00 ` [TUHS] [SPAM] Re: FreeBSD behind the times? (was: Favorite unix design principles?) Bakul Shah
2021-02-09 2:15 ` [TUHS] " Will Senn
2021-02-09 2:16 ` Will Senn
2021-02-09 2:30 ` Greg 'groggy' Lehey
2021-01-31 0:39 ` Steve Nickolas
2021-01-31 1:47 ` Will Senn
2021-01-31 2:25 ` Larry McVoy
2021-01-31 2:52 ` Will Senn
2021-01-31 3:00 ` Larry McVoy
2021-01-31 3:06 ` Will Senn
2021-01-31 3:32 ` John Cowan
2021-02-04 5:43 ` Dave Horsfall
2021-02-04 6:10 ` Angus Robinson
2021-02-04 7:46 ` Andy Kosela
2021-02-04 22:25 ` Dave Horsfall
2021-02-04 15:45 ` Will Senn
2021-02-04 16:03 ` Henry Bent
2021-02-04 16:32 ` Dan Cross
2021-02-04 16:49 ` Will Senn
2021-02-04 17:46 ` Larry McVoy
2021-02-04 18:41 ` Bakul Shah
2021-02-04 22:28 ` George Michaelson
2021-02-04 22:41 ` Bakul Shah
2021-02-05 0:33 ` Larry McVoy
2021-02-05 5:17 ` Bakul Shah
2021-02-05 14:18 ` Larry McVoy [this message]
2021-02-05 18:16 ` Warner Losh
2021-02-05 18:21 ` ron minnich
2021-02-06 0:03 ` Bakul Shah
2021-02-06 2:06 ` Dan Cross
2021-02-06 3:01 ` Bakul Shah
2021-02-06 1:18 ` John Gilmore
2021-02-06 1:43 ` joe mcguckin
2021-02-06 1:55 ` Bakul Shah
2021-02-05 20:50 ` Dave Horsfall
2021-02-06 0:21 ` Brad Spencer
2021-02-06 2:22 ` Rico Pajarola
2021-02-06 2:55 ` Larry McVoy
2021-02-06 3:07 ` Will Senn
2021-02-27 8:54 ` Stuart Remphrey
2021-02-06 4:55 ` John Cowan
2021-02-04 7:46 ` Chris Torek
2021-02-04 15:47 ` Will Senn
2021-02-11 21:01 ` Angel M Alganza
2021-01-30 23:09 ` [TUHS] Favorite unix design principles? John Cowan
2021-01-30 23:22 ` Jon Steinhart
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