[parisc-linux] Re: Problems with kernel mmap (failing tst-mmap-eofsync in glibc on parisc)

[Matthew Wilcox]

On Fri, Aug 22, 2003 at 09:14:47AM -0700, David S. Miller wrote:
> On 22 Aug 2003 09:40:37 -0500
> James Bottomley <James.Bottomley@SteelEye.com> wrote:
> > The reason this doesn't happen is because the mapping is not on the
> > mmap_shared list that flush_dcache_page() updates.
> 
> flush_dcache_page() checks both the shared and non-shared mmap lists,
> so if it is on _either_ list it is flushed.  It does not check only
> the shared list.

Gah, that's going to get really inefficient.  I still think we want to
split flush_dcache_page() into two operations -- flush_dcache_user() and
flush_dcache_kernel().  flush_dcache_user() would flush this specific
user mapping back to ram and flush_dcache_kernel() would flush the
kernel mapping.  Obviously we'd still want to have flush_dcache_page()
as there are instances when you want to flush all user mappings and the
kernel mapping back to ram.

> The VM_SHARED change you are proposing is definitely wrong.

Why is it wrong?  Why should whether-or-not a mapping is read-only affect
whether it's mapped shared?  I can't see anything in SuS v3 that suggests
we should do this.

-- 
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