On Wed, Jan 15, 2025 at 11:31:29AM +0200, Kirill A. Shutemov wrote:
> -static void lru_deactivate_file(struct lruvec *lruvec, struct folio *folio)
> -{
> - bool active = folio_test_active(folio) || lru_gen_enabled();
> - long nr_pages = folio_nr_pages(folio);
> -
> - if (folio_test_unevictable(folio))
> - return;
> -
> - /* Some processes are using the folio */
> - if (folio_mapped(folio))
> - return;
> -
> - lruvec_del_folio(lruvec, folio);
> - folio_clear_active(folio);
> - folio_clear_referenced(folio);
> -
> - if (folio_test_writeback(folio) || folio_test_dirty(folio)) {
> - /*
> - * Setting the reclaim flag could race with
> - * folio_end_writeback() and confuse readahead. But the
> - * race window is _really_ small and it's not a critical
> - * problem.
> - */
> - lruvec_add_folio(lruvec, folio);
> - folio_set_reclaim(folio);
> - } else {
> - /*
> - * The folio's writeback ended while it was in the batch.
> - * We move that folio to the tail of the inactive list.
> - */
> - lruvec_add_folio_tail(lruvec, folio);
> - __count_vm_events(PGROTATED, nr_pages);
> - }
> -
> - if (active) {
> - __count_vm_events(PGDEACTIVATE, nr_pages);
> - __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
> - nr_pages);
> - }
> -}
> +++ b/mm/truncate.c
> @@ -486,7 +486,7 @@ unsigned long mapping_try_invalidate(struct address_space *mapping,
> * of interest and try to speed up its reclaim.
> */
> if (!ret) {
> - deactivate_file_folio(folio);
> + folio_set_dropbehind(folio);
brr.
This is a fairly substantial change in semantics, and maybe it's fine.
At a high level, we're trying to remove pages from an inode that aren't
in use. But we might find that some of them are in use (eg they're
mapped or under writeback). If they are mapped, we don't currently
try to accelerate their reclaim, but now we're going to mark them
as dropbehind. I think that's wrong.
If they're dirty or under writeback, then yes, mark them as dropbehind, but
I think we need to be a little more surgical here. Maybe preserve the
unevictable check too.
