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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Yu Zhao , Kairui Song , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Hui Zhu Subject: [PATCH v2] mm/mglru: fix a no-op lru_gen_clear_refs() call in lru_lazyfree() Date: Mon, 26 Oct 2026 16:40:35 +0800 Message-ID: <20261026084035.535989-1-hui.zhu@linux.dev> X-Mailer: git-send-email 2.53.0 X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 8F1B41C0002 X-Rspam-User: X-Stat-Signature: ccppk3rsrbhmq4hbcni83cx96thxk9wi X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1793004047-163997 X-HE-Meta: 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 hU83Ks+s qpDTmNSEe3snz+XfiK2XIoonjCF1KXaEMj6ZM/ViKfksAG0T8LcmNxOgm9pZmR/6G3M2honGETHUYJmqRlr3GGFl7Dl7a83PJEmUU4cvt0OIh9hdPak3KTUgqX287yhjsVz+sf7xq3H4L/y+MFUSNgKsKYC4lAke/Vu6z6ieLwrPoZSjcPtEmYwjGf52HfyNL/fQYIvjhszZzu0OaMZPWwT/zrUuwDu07pngnAMrrw7SUhwF0i6+sHAW4tZzNP32MJwWOD8Mt+J+XBpWkJTizvEUh2z+VpozrlY3gLt1WAceJeg4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 From: Hui Zhu lru_lazyfree() calls lru_gen_clear_refs() after lruvec_del_folio(), but lru_gen_del_folio() has already cleared LRU_GEN_MASK, so folio_lru_gen() returns -1 and lru_gen_clear_refs() exits at its "gen < 0" check without clearing the refs or PG_workingset. A MADV_FREE folio therefore keeps the state it had before madvise(2), even though madvise_free_pte_range() has already cleared the accessed and dirty bits of its PTEs. lru_gen_folio_seq() places it one generation younger, and PG_workingset puts it in the last tier, so sort_folio() promotes and protects it instead of evicting it and charges it to lrugen->protected[], which read_ctrl_pos() uses to balance anon against file reclaim. __folio_inc_gen() clears the refs but not PG_workingset, so this repeats every time the folio reaches the oldest generation. If the folio is redirtied first, ttu_anon_lazyfree_folio() keeps it and lru_gen_eviction() packs the stale state into the shadow entry, so a later refault is promoted to the youngest generation. Call lru_gen_clear_refs() while the folio is still on the generation list, as deactivate_file_folio() and folio_deactivate() already do. Its return value only says whether the folio is in the oldest generation, which lru_lazyfree() does not need because it re-adds the folio below. Keep folio_clear_referenced() unconditional: the classic LRU needs it, and it also covers the folios that lru_gen_clear_refs() skips. Fixes: cc8ec7be78ff ("mm/mglru: optimize deactivation") Suggested-by: Barry Song Signed-off-by: Hui Zhu --- Changelog: v2: Call lru_gen_clear_refs() before lruvec_del_folio() instead of open-coding the flag clears; drop the lru_gen_enabled() branch and the comment (Barry Song). mm/folio.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/mm/folio.c b/mm/folio.c index 35e242b48870..ea3adb6a89d7 100644 --- a/mm/folio.c +++ b/mm/folio.c @@ -597,12 +597,10 @@ static void lru_lazyfree(struct lruvec *lruvec, struct folio *folio) folio_test_swapcache(folio) || folio_test_unevictable(folio)) return; + lru_gen_clear_refs(folio); lruvec_del_folio(lruvec, folio); folio_clear_active(folio); - if (lru_gen_enabled()) - lru_gen_clear_refs(folio); - else - folio_clear_referenced(folio); + folio_clear_referenced(folio); /* * Lazyfree folios are clean anonymous folios. They have * the swapbacked flag cleared, to distinguish them from normal -- 2.53.0