On Mon, Mar 11, 2024 at 11:01 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > Now that swap supports storing all mTHP sizes, avoid splitting large > folios before swap-out. This benefits performance of the swap-out path > by eliding split_folio_to_list(), which is expensive, and also sets us > up for swapping in large folios in a future series. > > If the folio is partially mapped, we continue to split it since we want > to avoid the extra IO overhead and storage of writing out pages > uneccessarily. > > Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> > --- > mm/vmscan.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index cf7d4cf47f1a..0ebec99e04c6 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1222,11 +1222,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, > if (!can_split_folio(folio, NULL)) > goto activate_locked; > /* > - * Split folios without a PMD map right > - * away. Chances are some or all of the > - * tail pages can be freed without IO. > + * Split partially mapped folios map > + * right away. Chances are some or all > + * of the tail pages can be freed > + * without IO. > */ > - if (!folio_entire_mapcount(folio) && > + if (!list_empty(&folio->_deferred_list) && Hi Ryan, After reconsidering our previous discussion about PMD-mapped large folios, I've pondered the possibility of PMD-mapped Transparent Huge Pages (THPs) being mapped by multiple processes. In such a scenario, if one process decides to unmap a portion of the folio while others retain the entire mapping, it raises questions about how the system should handle this situation. Would the large folio be placed in a deferred list? If so, splitting it might not yield benefits, as neither I/O nor swap slots would increase in this case by not splitting it. Regarding PTE-mapped large folios, the absence of an indicator like "entire_map" makes it challenging to identify cases where the entire folio is mapped. Thus, splitting seems to be the only viable solution in such circumstances. > split_folio_to_list(folio, > folio_list)) > goto activate_locked; > -- > 2.25.1 Thanks Barry
