On Mon, 2017-03-13 at 11:44 -0400, Zi Yan wrote: > From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > > 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, bits 1-4 are not used in non-present format > since commit 00839ee3b299 ("x86/mm: Move swap offset/type up in PTE to > work around erratum"). So let's move _PAGE_SWP_SOFT_DIRTY to bit 1. > Bit 7 is used as reserved (always clear), so please don't use it for > other purpose. > > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Signed-off-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx> > --- > arch/x86/include/asm/pgtable_64.h | 12 +++++++++--- > arch/x86/include/asm/pgtable_types.h | 10 +++++----- > 2 files changed, 14 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h > index 73c7ccc38912..a5c4fc62e078 100644 > --- a/arch/x86/include/asm/pgtable_64.h > +++ b/arch/x86/include/asm/pgtable_64.h > @@ -157,15 +157,21 @@ static inline int pgd_large(pgd_t pgd) { return 0; } > /* > * Encode and de-code a swap entry > * > - * | ... | 11| 10| 9|8|7|6|5| 4| 3|2|1|0| <- bit number > - * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P| <- bit names > - * | OFFSET (14->63) | TYPE (9-13) |0|X|X|X| X| X|X|X|0| <- swp entry > + * | ... | 11| 10| 9|8|7|6|5| 4| 3|2| 1|0| <- bit number > + * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U| W|P| <- bit names > + * | OFFSET (14->63) | TYPE (9-13) |0|0|X|X| X| X|X|SD|0| <- swp entry > * > * G (8) is aliased and used as a PROT_NONE indicator for > * !present ptes. We need to start storing swap entries above > * there. We also need to avoid using A and D because of an > * erratum where they can be incorrectly set by hardware on > * non-present PTEs. > + * > + * SD (1) in swp entry is used to store soft dirty bit, which helps us > + * remember soft dirty over page migration > + * > + * Bit 7 in swp entry should be 0 because pmd_present checks not only P, > + * but also G. but also L and G. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>