On Mon, 2005-11-21 at 15:34 -0800, Andrew Morton wrote:
> Trond Myklebust <[email protected]> wrote:
> >
> > Anything that calls lock_page() should be avoided in O_DIRECT,
>
> Why?
>
> And it's still doing lock_page():
>
> nfs_file_direct_write()
> ->filemap_fdatawrite()
> ->do_writepages()
> ->nfs_writepages()
> ->generic_writepages()
> ->mpage_writepages()
> ->lock_page()
True.
> > however
> > we should be able to call invalidate_inode_pages() since that doesn't
> > wait on the page lock.
>
> invalidate_inode_pages2() is better.
> And using generic_file_direct_IO() is
> better still, since it handles mmap coherency and only work upon that part
> of the file which is actually undergoing IO.
Unlike local filesystems, we don't want to have to take the i_sem in any
of the direct IO paths. The latter is just a liability as far as
applications are concerned: it doesn't offer any protection for local
data (there _is_ no local data to protect), but gets seriously in the
way of write parallelism.
The only difference I can see between the two paths is the call to
unmap_mapping_range(). What effect would that have?
Cheers,
Trond
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