From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.187 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793085912; b=zC0ymgZTMXy/HYVJEVKtM1PE2XFv2U+uU3lbL3buxao32HmwAr0JHzGaKcZk2qzPJM3v oHxZYQUTcjf8RYr6K+CgTctirYxv2wWbb6fnmfDRPzZFFIm+M2QItPWvHT451mcllH9X/ nWaajbJp2ii+65JCB1zdtjg7ygbiMOOXMBlQGPuwNLmIII6LY6w2ZAjQq2uuc+ZHDYO8o vq5zdlF+JBF7SnXBddtMpVPl+/3vNG1YtnNzMqWSKWEqf86o7VCzeHDgCI4rtKO/FBHdb MwBu7hxReEhhbkq8R4/3JF5dO3/4yM5UUYR3aO834uO2caxECZR0yUatBF68Qm6L84g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793085912; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=JYwlk5SABAXJfCGJC/CIrpBqm46Lfjo6fP+QGuM8Wo4=; b=SSfQoLHsyNRRolHpI6x4mJQw4A6fSEGM9JxeSB9CL4ETtRKjlaeJXG6H7ALRH1EqMXe4 fkqRF5leNfIMjeF9XyGvG1Un3N96NxJOakw10v6O7twem6FXfmxaAwDOO+W8Ikuw8KsCT 0MgS8VrzlqN632Yvb8fTi5emCZwacxKYeBbXVVLK5lNxTdXSpz/5dseuUVVdC8T7RuLNs 0jlC5/IKpnHOaBMcFnouCU7GQs5KqTkiQp+HppoffuLzv0Gu1ButwowDAnnd/htHy3aXn Sw4yhp2vBbcjDRKyQSddwEMPBQ+YbL6oRG2LTDBpjsPkLExqLQcc0JRdqrrXIlzw10Q== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=A64+ePD3; arc=none smtp.remote-ip=91.218.175.187 Received: from mta0.migadu.com (out-187.mta0.migadu.com [91.218.175.187]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1D627606A31A for ; Tue, 27 Oct 2026 07:25:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 1D627606A31A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=A64+ePD3 X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=3EH6ZExPcZqz0wmFi1VNDDcCIIEYlOenwQf5HgNEt+M=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793085908; v=1; x=1793690708; b=A64+ePD3rRIeAuP/4lB71nO4+tOkGiryYLOgek3aUTDrus5Zed53htjDTY4vHmDQfyiZmmBb NKXLXxVXEWi6tp6rS1ZDIHUujL/XAVA9heHTfwzTokOBngqM0DYOFKsL9WoyEVZJwgFe/3TsISN ymlG9Ovu7hW8MYjormJF8xWQ= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 079adf22c9d54636; Tue, 27 Oct 2026 07:25:07 +0000 X-Mizu-Trace-ID: 079adf22c9d54636 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Tue, 27 Oct 2026 15:24:59 +0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Betterbird (macOS/Intel) Subject: Re: [PATCH v2] mm/mglru: fix a no-op lru_gen_clear_refs() call in lru_lazyfree() To: Barry Song Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Yu Zhao , Kairui Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hui Zhu References: <20261026084035.535989-1-hui.zhu@linux.dev> Content-Language: en-US From: Hui Zhu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 2026/10/26 17:47, Barry Song: > On Mon, Oct 26, 2026 at 4:40 PM Hui Zhu wrote: >> 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); > The only thing I'm not sure about is whether we need > if (lru_gen_enabled()) here to keep the semantics consistent > with other places where we use it. > > ... > 2 676 mm/folio.c <> > if (lru_gen_enabled() && lru_gen_clear_refs(folio)) > 3 695 mm/folio.c <> > if (lru_gen_enabled() ? lru_gen_clear_refs(folio) : > !folio_test_active(folio)) > > So maybe we still need > > + if (lru_gen_enabled()) > lru_gen_clear_refs(folio); I think we maybe don't need it here.  The other two sites consume the return value, and that is what the check disambiguates:     if (gen < 0)         return true; An off-list folio has gen == -1, so without lru_gen_enabled() both deactivate_file_folio() and folio_deactivate() would take that "true" and return early, skipping the deactivation.  lru_lazyfree() ignores the return value, since it re-adds the folio a few lines below anyway. The side effects gate themselves, and on something more precise than the global key: a folio on a classic list always has gen == -1, which fill_evictable() even asserts,     VM_WARN_ON_ONCE_FOLIO(folio_lru_gen(folio) != -1, folio); and drain_evictable() clears LRU_GEN_MASK on the way out.  So an unguarded call either clears the refs of a folio that is on a generation list, or does nothing at all - no flag writes and no lruvec access.  The classic LRU cannot be affected, including with CONFIG_LRU_GEN=n, where the stub inlines away. Guarding on the key would reopen a narrower version of this bug. lru_gen_change_state() flips it before migrating any folio:     if (enabled) static_branch_enable_cpuslocked(&lru_gen_caps[LRU_GEN_CORE]);     else static_branch_disable_cpuslocked(&lru_gen_caps[LRU_GEN_CORE]);     memcg = mem_cgroup_iter(NULL, NULL, NULL); so while MGLRU is being turned off the key is already false, but every lruvec that drain_evictable() has not reached yet still has its folios on generation lists.  A MADV_FREE batch drained on another CPU in that window would keep PG_workingset. What about add a comment instead of the check:     /* no-op unless the folio is on a generation list */     lru_gen_clear_refs(folio); Best, Hui > > with that, feel free to add: > > Reviewed-by: Barry Song