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From: ron minnich <rminnich@gmail.com>
To: Larry McVoy <lm@mcvoy.com>
Cc: Bakul Shah <bakul@iitbombay.org>, TUHS main list <tuhs@minnie.tuhs.org>
Subject: Re: [TUHS] FreeBSD behind the times? (was: Favorite unix design principles?)
Date: Fri, 5 Feb 2021 10:21:54 -0800	[thread overview]
Message-ID: <CAP6exYKL5sEFonOjyGgEXBtBZRRKVbZX7buDne9yhY3bzBj5rg@mail.gmail.com> (raw)
In-Reply-To: <20210205141820.GO13701@mcvoy.com>

I think hearing *why* they did that would be interesting.

On Fri, Feb 5, 2021 at 6:19 AM Larry McVoy <lm@mcvoy.com> wrote:
>
> 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.

  parent reply	other threads:[~2021-02-05 18:22 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
2021-02-05 18:16                                         ` Warner Losh
2021-02-05 18:21                                         ` ron minnich [this message]
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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