Re: [RFC PATCH] ARM: Assume new page cache pages have dirty D-cache

Paul Mundt
2010-03-05T01:29:06Z

On Thu, Mar 04, 2010 at 09:44:35PM +0000, Russell King - ARM Linux wrote:
> On Thu, Mar 04, 2010 at 06:36:42PM +0000, Catalin Marinas wrote:
> > ARM: Assume new page cache pages have dirty D-cache
> >
> > From: Catalin Marinas <catalin.marinas@arm.com>
> >
> > There are places in Linux where writes to newly allocated page cache
> > pages happen without a subsequent call to flush_dcache_page() (several
> > PIO drivers including USB HCD). This patch changes the meaning of
> > PG_arch_1 to be PG_dcache_clean and always flush the D-cache for a newly
> > mapped page in update_mmu_cache().
> >
> > The patch also sets the PG_arch_1 bit in the DMA cache maintenance
> > function to avoid additional cache flushing in update_mmu_cache().
>
> As I just realised, this is going to subject all pages placed into
> userspace with a D cache flush - even anonymous pages, and those
> which we've been careful to deal with the cache issues already (eg,
> via the COW page copying code.)
>
> I think all the copypage functions need to set PG_dcache_clean on the
> new pages once their copy has completed.
>
> I wonder if there's any other anonymous page creating functions which
> could do with a similar treatment...

In the anonymous page case, flush_anon_page() is always called prior to
flush_dcache_page(), so flush_anon_page() could just set PG_dcache_clean
to work around that. That would handle get_user_pages(), too.