From: "David S. Miller" <davem@redhat.com>
To: James Bottomley <James.Bottomley@SteelEye.com>
Cc: hugh@veritas.com, willy@debian.org, linux-kernel@vger.kernel.org,
parisc-linux@lists.parisc-linux.org, drepper@redhat.com
Subject: Re: [parisc-linux] Re: Problems with kernel mmap (failing tst-mmap-eofsync in glibc on parisc)
Date: Sat, 23 Aug 2003 14:43:30 -0700 [thread overview]
Message-ID: <20030823144330.5ddab065.davem@redhat.com> (raw)
In-Reply-To: <1061600974.2090.809.camel@mulgrave>
On 22 Aug 2003 20:09:30 -0500
James Bottomley <James.Bottomley@SteelEye.com> wrote:
> What we were hoping is that we could rely on this little property of
> mmap:
>
> MAP_PRIVATE
> Create a private copy-on-write mapping. Stores
> to the region do not affect the original file.
> It is unspecified whether changes made to the
> file after the mmap call are visible in the
> mapped region.
>
> To avoid having to flush the non-shared mappings (basically on parisc if
> you write to a file backing a MAP_PRIVATE mapping then we don't
> guarantee you see the update).
>
> I suppose if we had a way of telling if any of the i_mmap list members
> were really MAP_SHARED semantics mappings, then we could alter our
> flush_dcache_page() implementation to work.
I thought about this very deeply last night and this morning.
And what you're trying to optimize won't work. Here is why.
If the first access to a MAP_PRIVATE mapping of a page is a read,
we'll use the page-cache page. This means that, with your
optimization, during this time if another cpu write()`s into the
page we'll lose the data update.
Sorry :(
next prev parent reply other threads:[~2003-08-23 21:51 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-08-22 14:40 Problems with kernel mmap (failing tst-mmap-eofsync in glibc on parisc) James Bottomley
2003-08-22 16:14 ` David S. Miller
2003-08-22 16:34 ` [parisc-linux] " Matthew Wilcox
2003-08-22 16:39 ` David S. Miller
2003-08-22 17:41 ` Matthew Wilcox
2003-08-22 17:36 ` David S. Miller
2003-08-22 18:01 ` David S. Miller
2003-08-22 18:34 ` Hugh Dickins
2003-08-22 18:31 ` David S. Miller
2003-08-22 18:56 ` James Bottomley
2003-08-22 19:19 ` David S. Miller
2003-08-22 22:27 ` James Bottomley
2003-08-22 22:41 ` David S. Miller
2003-08-23 1:09 ` James Bottomley
2003-08-23 7:22 ` Hugh Dickins
2003-08-23 15:59 ` James Bottomley
2003-08-23 21:44 ` David S. Miller
2003-08-23 21:43 ` David S. Miller [this message]
2003-08-23 22:21 ` James Bottomley
2003-08-23 22:51 ` David S. Miller
2003-08-23 23:01 ` James Bottomley
2003-08-23 22:53 ` David S. Miller
2003-08-23 23:11 ` James Bottomley
2003-08-24 0:22 ` David S. Miller
[not found] ` <1061702282.1992.1153.camel@mulgrave>
[not found] ` <20030823222300.4695a0c4.davem@redhat.com>
2003-08-24 16:54 ` James Bottomley
2003-08-22 18:41 ` James Bottomley
2003-08-22 19:02 ` Hugh Dickins
2003-08-22 19:09 ` Randolph Chung
2003-08-22 16:42 ` Russell King
2003-08-22 16:39 ` David S. Miller
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