<alexlzhu@xxxxxx> writes: > From: Alexander Zhu <alexlzhu@xxxxxx> > > Currently, when /sys/kernel/mm/transparent_hugepage/enabled=always is set > there are a large number of transparent hugepages that are almost entirely > zero filled. This is mentioned in a number of previous patchsets > including: > https://lore.kernel.org/all/20210731063938.1391602-1-yuzhao@xxxxxxxxxx/ > https://lore.kernel.org/all/ > 1635422215-99394-1-git-send-email-ningzhang@xxxxxxxxxxxxxxxxx/ > > Currently, split_huge_page() does not have a way to identify zero filled > pages within the THP. Thus these zero pages get remapped and continue to > create memory waste. In this patch, we identify and free tail pages that > are zero filled in split_huge_page(). In this way, we avoid mapping these > pages back into page table entries and can free up unused memory within > THPs. This is based off the previously mentioned patchset by Yu Zhao. > However, we chose to free anonymous zero tail pages whenever they are > encountered instead of only on reclaim or migration. > > We also add self tests to verify the RssAnon value to make sure zero > pages are not remapped except in the case of userfaultfd. In the case > of userfaultfd we remap to the shared zero page, similar to what is > done by KSM. > > Signed-off-by: Alexander Zhu <alexlzhu@xxxxxx> > --- > include/linux/rmap.h | 2 +- > include/linux/vm_event_item.h | 3 + > mm/huge_memory.c | 44 ++++++- > mm/migrate.c | 72 +++++++++-- > mm/migrate_device.c | 4 +- > mm/vmstat.c | 3 + > .../selftests/vm/split_huge_page_test.c | 113 +++++++++++++++++- > tools/testing/selftests/vm/vm_util.c | 23 ++++ > tools/testing/selftests/vm/vm_util.h | 1 + > 9 files changed, 250 insertions(+), 15 deletions(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index b89b4b86951f..f7d5d5639dea 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -372,7 +372,7 @@ int folio_mkclean(struct folio *); > int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff, > struct vm_area_struct *vma); > > -void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked); > +void remove_migration_ptes(struct folio *src, struct folio *dst, bool locked, bool unmap_clean); There are 2 bool parameters now. How about use "flags" style parameters? IMHO, well defined constants are more readable than a set of true/false. Best Regards, Huang, Ying [snip]
