On Thu, 23 Aug 2012 18:36:02 +0100
Will Deacon [off-list ref] wrote:

On Thu, Aug 23, 2012 at 06:11:56PM +0100, Michal Hocko wrote:

quoted

On Thu 23-08-12 17:37:13, Will Deacon wrote:

quoted

The core page allocator ensures that page flags are zeroed when freeing
pages via free_pages_check. A number of architectures (ARM, PPC, MIPS)
rely on this property to treat new pages as dirty with respect to the
data cache and perform the appropriate flushing before mapping the pages
into userspace.

This can lead to cache synchronisation problems when using hugepages,
since the allocator keeps its own pool of pages above the usual page
allocator and does not reset the page flags when freeing a page into
the pool.

This patch adds a new architecture hook, arch_clear_hugepage_flags, so
that architectures which rely on the page flags being in a particular
state for fresh allocations can adjust the flags accordingly when a
page is freed into the pool.

You could have used __weak here quite neatly, but whatever.

Next step: start posting the ARM code!

I suggest you keep this patch in whichever tree holds that arm code.  If
I see this patch turn up in linux-next then I'll just drop my copy,
expecting that this patch will be merged alongside the ARM changes.

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