On Thu, Nov 10, 2016 at 03:29:51PM -0800, Dave Hansen wrote: > On 11/07/2016 03:31 PM, Naoya Horiguchi wrote: > > pmd_present() checks _PAGE_PSE along with _PAGE_PRESENT to avoid false > > negative > > return when it races with thp spilt (during which _PAGE_PRESENT is temporary > > cleared.) I don't think that dropping _PAGE_PSE check in pmd_present() works > > well because it can hurt optimization of tlb handling in thp split. > > In the current kernel, bit 6 is not used in non-present format because > > nonlinear > > file mapping is obsolete, so let's move _PAGE_SWP_SOFT_DIRTY to that bit. > > Bit 7 is used as reserved (always clear), so please don't use it for other > > purpose. > ... > > #ifdef CONFIG_MEM_SOFT_DIRTY > > -#define _PAGE_SWP_SOFT_DIRTY _PAGE_PSE > > +#define _PAGE_SWP_SOFT_DIRTY _PAGE_DIRTY > > #else > > #define _PAGE_SWP_SOFT_DIRTY (_AT(pteval_t, 0)) > > #endif > > I'm not sure this works. Take a look at commit 00839ee3b29 and the > erratum it works around. I _think_ this means that a system affected by > the erratum might see an erroneous _PAGE_SWP_SOFT_DIRTY/_PAGE_DIRTY get > set in swap ptes. > > There are much worse things that can happen, but I don't think bits 5 > (Accessed) and 6 (Dirty) are good choices since they're affected by the > erratum.
Thank you for the information. According to 00839ee3b29, some bits which are safe from the errata are reclaimed, so assigning one of such bits for _PAGE_SWP_SOFT_DIRTY seems to work. And I'll update the description. Thanks, Naoya Horiguchi
