Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> wrote: > From: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com> > > When we collapse normal pages to hugepage, we first clear the pmd, then > invalidate all > the PTE entries. The assumption here is that any low level page fault will > see pmd as > none and take the slow path that will wait on mmap_sem. But we could very > well be in > a hash_page with local ptep pointer value. Such a hash page can result in > adding new > HPTE entries for normal subpages/small page. That means we could be modifying > the > page content as we copy them to a huge page. Fix this by waiting on hash_page > to finish > after marking the pmd none and bfore invalidating HPTE entries. We use the > heavy > kick_all_cpus_sync(). This should be ok as we do this in the background > khugepaged > thread and not in application context. But we block page fault handling for > this time. > Also if we find collapse slow we can ideally increase the scan rate.
80 columns here > > Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> > --- > arch/powerpc/mm/pgtable_64.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c > index bbecac4..4bb44c3 100644 > --- a/arch/powerpc/mm/pgtable_64.c > +++ b/arch/powerpc/mm/pgtable_64.c > @@ -543,6 +543,14 @@ pmd_t pmdp_clear_flush(struct vm_area_struct *vma, > unsigned long address, > pmd = *pmdp; > pmd_clear(pmdp); > /* > + * Wait for all pending hash_page to finish > + * We can do this by waiting for a context switch to happen on > + * the cpus. Any new hash_page after this will see pmd none > + * and fallback to code that takes mmap_sem and hence will block > + * for collapse to finish. > + */ > + kick_all_cpus_sync(); > + /* This doesn't apply on mainline... I assume it's needs your TPH patches? Also, dumb question. Is this a bug we're fixing or just an optimisation? Mikey > * Now invalidate the hpte entries in the range > * covered by pmd. This make sure we take a > * fault and will find the pmd as none, which will > -- > 1.8.1.2 > > _______________________________________________ > Linuxppc-dev mailing list > Linuxppc-dev@lists.ozlabs.org > https://lists.ozlabs.org/listinfo/linuxppc-dev > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
