Re: [RFT][PATCH 0/2] pagefault scalability alternative

[Nick Piggin <nickpiggin@yahoo.com.au>]

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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