On Sat, Apr 20, 2024 at 12:59 PM Lance Yang <ioworker0@xxxxxxxxx> wrote: > > Hey Matthew, > > Thanks for taking time to review! > > On Wed, Apr 17, 2024 at 11:09 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Wed, Apr 17, 2024 at 10:11:11PM +0800, Lance Yang wrote: > > > When the user no longer requires the pages, they would use madvise(madv_free) > > > to mark the pages as lazy free. IMO, they would not typically rewrite to the > > > given range. > > > > > > At present, a PMD-mapped THP marked as lazyfree during shrink_folio_list() > > > is unconditionally split, which may be unnecessary. If the THP is exclusively > > > mapped and clean, and the PMD associated with it is also clean, then we can > > > attempt to remove the PMD mapping from it. This change will improve the > > > efficiency of memory reclamation in this case. > > > > > > On an Intel i5 CPU, reclaiming 1GiB of PMD-mapped THPs using > > > mem_cgroup_force_empty() results in the following runtimes in seconds > > > (shorter is better): > > > > > > -------------------------------------------- > > > | Old | New | Change | > > > -------------------------------------------- > > > | 0.683426 | 0.049197 | -92.80% | > > > -------------------------------------------- > > > > > > Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx> > > > --- > > > include/linux/huge_mm.h | 1 + > > > include/linux/rmap.h | 1 + > > > mm/huge_memory.c | 2 +- > > > mm/rmap.c | 81 +++++++++++++++++++++++++++++++++++++++++ > > > mm/vmscan.c | 7 ++++ > > > 5 files changed, 91 insertions(+), 1 deletion(-) > > > > I'm confused why we need all this extra code. If we remove a folio > > Thanks for pointing that out! > > I've added a lot of extra code to rmap.c, and we don't need it > for file pages - sorry. I'll reconsider where to place this code. > > > from the pagecache, we can just call truncate_inode_folio() and > > unmap_mapping_folio() takes care of all the necessary unmappings. > > Why can't you call unmap_mapping_folio() here? > > Thanks for your suggestion. > > But this change only avoids the splitting of *anon* large folios > (PMD-mapped THPs) that are marked as lazyfree during > shrink_folio_list(). > > IIUC, in some cases, we cannot unmap the THP marked as lazyfree > here, such as when it's not exclusively mapped, dirty, pinned, etc. I’d like to make a correction. IMO, we can unmap the THP that is not exclusively mapped, but ensuring folio_ref_count() equals folio_mapcount() +1. Thanks, Lance > In such situations, we still need to return to try_to_unmap_one(), and > then call split_huge_pmd_address() to split it. > > Thanks again for the review. > Lance
