Christoph Lameter wrote:

The patch generally drops the first acquisition of the page 
table lock from handle_mm_fault that is used to protect the read 
operations on the page table. I doubt that this works with i386 PAE since 
the page table read operations are not protected by the ptl. These are 64 
bit which cannot be reliably retrieved in an 32 bit operation on i386 as 
you pointed out last fall. There may be concurrent writes so that one 
gets two pieces that do not fit. PAE mode either needs to fall back to 
take the page_table_lock for reads or use some tricks to guarantee 64bit 
atomicity.

Oh yes, you need 64-bit atomic reads and writes for that.

We actually did see that load in handle_pte_fault being cut
in half by a store.

I wouldn't be too worried about that though, as it's only
for PAE.

-- 
SUSE Labs, Novell Inc.

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