Messages in this thread | | | Date | Wed, 30 May 2012 16:01:51 -0400 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [PATCH 04/35] autonuma: define _PAGE_NUMA_PTE and _PAGE_NUMA_PMD |
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On Wed, May 30, 2012 at 08:34:06PM +0200, Andrea Arcangeli wrote: > Hi Konrad, > > On Wed, May 30, 2012 at 02:22:49PM -0400, Konrad Rzeszutek Wilk wrote: > > Thank you for loking at this from the xen side. The interesting thing > > is that I believe the _PAGE_PAT (or _PAGE_PSE) is actually used on > > Xen on PTEs. It is used to mark the pages WC. <sigh> > > Oops, I'm using _PAGE_PSE too on the pte, but only when it's unmapped. > > static inline int pte_numa(pte_t pte) > { > return (pte_flags(pte) & > (_PAGE_NUMA_PTE|_PAGE_PRESENT)) == _PAGE_NUMA_PTE; > } > > And _PAGE_UNUSED2 (_PAGE_IOMAP) is used for the pmd but _PAGE_IOMAP by > Xen should only be set on ptes. <nods> > > The only way to use _PAGE_PSE safe on the pte is if the pte is > non-present, is this what Xen is also doing? (in turn colliding with > pte_numa)
The only time the _PAGE_PSE (_PAGE_PAT) is set is when _PAGE_PCD | _PAGE_PWT are set. It is this ugly transformation of doing:
if (pat_enabled && _PAGE_PWT | _PAGE_PCD) pte = ~(_PAGE_PWT | _PAGE_PCD) | _PAGE_PAT;
and then writting the pte with the 7th bit set instead of the 2nd and 3rd to mark it as WC. There is a corresponding reverse too (to read the pte - so the pte_val calls) - so if _PAGE_PAT is detected it will remove the _PAGE_PAT and return the PTE as if it had _PAGE_PWT | _PAGE_PCD.
So that little bit of code will need some tweaking - as it does that even if _PAGE_PRESENT is not set. Meaning it would transform your _PAGE_PAT to _PAGE_PWT | _PAGE_PCD. Gah!
> > Now if I shrink the size of the page_autonuma to one entry per pmd > (instead of per pte) I may as well drop pte_numa entirely and only > leave pmd_numa. At the moment it's possible to switch between the two > models at runtime with sysctl (if one wants to do a more expensive > granular tracking). I'm still uncertain on the best way to shrink > the page_autonuma size we'll see.
OK. I can whip up a patch to deal with the 'Gah!' case easily if needed.
Thanks!
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