Michael Neuling <mi...@neuling.org> writes: > 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?
yes, They are on top V10 THP series > > Also, dumb question. Is this a bug we're fixing or just an optimisation? This is a bug fix. The details can be found at http://article.gmane.org/gmane.linux.ports.ppc.embedded/60266 -aneesh _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
