On Mon, 2007-07-16 at 17:03 -0500, James Bottomley wrote:
> On Tue, 2007-07-17 at 07:49 +1000, Benjamin Herrenschmidt wrote:
> > > No ... that was the point of flush_kernel_dcache_page(). The page in
> > > question is page cache backed and contains user mappings. However, the
> > > block layer has already done a flush_dcache_page() in get_user_pages()
> > > and the user shouldn't be touching memory under I/O (unless they want
> > > self induced aliasing problems) so we're free to assume all the user
> > > cachelines are purged, hence all we have to do is flush the kernel alias
> > > to bring the page up to date and make the users see it correctly.
> >
> > The block layer will have done that even in the swap-out path ? (Just
> > asking... I'm not very familiar with the block layer)
>
> Er ... not really, this is the I/O path for user initiated I/O. The
> page out path, by definition, can't have any extant user mappings. For
> page out, the relevant page is flushed before its mapping is detached,
> and then it can be paged to the backing store (or for anonymous pages to
> the swap device) when no mappings remain.
Ok, thanks.
Ben.
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