Re: [patch] fs: improved handling of page and buffer IO errors

[steve@chygwyn.com]

Hi,

On Tue, Oct 21, 2008 at 06:20:17PM +0200, Miklos Szeredi wrote:
> On Tue, 21 Oct 2008, steve@chygwyn.co wrote:
> > No, I guess it might be possible, but for the time being it is
> > its own "glock" plus the page lock dependency. I'd have to
> > think quite hard about what the consequences of using the
> > inode lock would be.
> > 
> > Of course we do demand the inode lock as well in some cases
> > since the vfs has already grabbed it before calling
> > into the filesystem when its required. Because of that and
> > where we run the glock state machine from, it would be rather
> > complicated to make that work I suspect,
> 
> BTW, why do you want strict coherency for memory mappings?  It's not
> something POSIX mandates.  It's not even something that Linux always
> did.
>
Its something that GFS has always done, and so we've tried to keep
that feature in GFS2. I think we do (at least I do) try to suggest
to people that they shouldn't be relying on this, but we've always
tried to make it work anyway, at least on the principle of least
surprise.
 
> If I were an application writer, I'd never try to rely on mmap
> coherency without the appropriate magic msync() calls.
> 
> Miklos

Yes, I'd agree, but I write kernel code, not applications :-)
Thanks for the explanation on splice, I'll take a look at that
code now and try to understand it in more detail,

Steve.

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