From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.243 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794448668; b=0Y1oyTeq0rRHt4jVTP52ax4o/j9P9SXSvTMyQULT5gda/RTVWYeMa2UPgDrGBdrZn4Io 3zwXMCQCjkpZC8vZuQlRFY5NgCTLezH4CJVG3p/VDSLlZ8IvT8HxadEhIx082+dBZ7uQT YVnq+D3z4eaUOyi0FnDN51XQdjAtwGOjlXjD+GEY6asDyo00r8zvz4s//CQMnfgv4hYQC 0NpcbpC+hifn0qxG6NVYpn1tufbAw9/iO5hkT72IKAXtEGZ9iUOJEe52NsgB2RrrBV9In 46NffNylxgDVAMYpZ1zPVcC2l9AubJkKRlIYVvWVvQXnURFaQFY6TKUKRz1HcI9xEYw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794448668; 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=gM036Lz3o4zVMa1LHZqyXfXI7ctHVwdatuzaP+xuoQk=; b=KE86quyhBCvGGVh084GQNMF0AJsHtVpe7djr7yH9s7T0+oaMiM2gwm4ZEtO1MNTrFHWC 9P6sh5WIrkm3e4DyYCEI/JhiV8EBimq8yU2yxMD1HdXZ05VmMcyPV4mO8ihGvlQbt3yaL VB54Zf71oeb/NHQ/FfUvNHOKIenJKTw1Qip1+LfGE+JffyfiD+kp6wtFmhP+cJeadPvDR KHPv3FLB4wwitt/6ipUsTbfASG9tsD10+73j5oaYdjfuwDYwmhZvzxXX9QSQYrkZNqMEp yZcNJMNNlJMryZy//b4L/tDV8+100Zq9DOwTly2sBsKyZyAp0kP34jo+mpkX4c96bwg== 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=faUooxKv; arc=none smtp.remote-ip=95.215.58.243 Received: from mta1.migadu.com (out-243.mta1.migadu.com [95.215.58.243]) (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 6A8C7606A883 for ; Thu, 12 Nov 2026 01:57:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 6A8C7606A883 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=faUooxKv X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=yKaM/QiUACyjX+qdRyFbfdqOOL/98E7TZUDAFfd2x+A=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794448665; v=1; x=1795053465; b=faUooxKv0kNDG903OFqeLVR1EGlcLCvX6gWu51FNniszxFnwsJRj5rGAm7y/bHE8ac1WigCr iDvPEllng7LoA7eG/DEUYyRb5kIo+/sIiNMhc3QOjJiyRL6/RdQLVeBFDwTiki0Zty3V4VAEiuZ hFjJVN1i5g23LdUhIj29ewqc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 41d9010a3529e826; Thu, 12 Nov 2026 01:57:45 +0000 X-Mizu-Trace-ID: 41d9010a3529e826 X-Migadu-Flow: FLOW_OUT Message-ID: <5e2733ee-7a25-430f-bdda-f89fc5856e5d@linux.dev> Date: Thu, 12 Nov 2026 09:57:35 +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 v3] mm/mglru: fix a no-op lru_gen_clear_refs() call in lru_lazyfree() To: "Liam R. Howlett" Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Yu Zhao , Kairui Song , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hui Zhu , stable@vger.kernel.org References: <20261109021611.22247-1-hui.zhu@linux.dev> <4xqyzrl4lbxwbky22lc5k5mcvusudg75z6hspjokfoghp3dny3@rjuukqzxiuyv> Content-Language: en-US From: Hui Zhu In-Reply-To: <4xqyzrl4lbxwbky22lc5k5mcvusudg75z6hspjokfoghp3dny3@rjuukqzxiuyv> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 2026/11/12 01:21, Liam R. Howlett: > On 26/11/09 10:16AM, 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") >> Cc: stable@vger.kernel.org >> Suggested-by: Barry Song >> Signed-off-by: Hui Zhu >> Reviewed-by: Barry Song > One nit.. > > Reviewed-by: Liam R. Howlett (Google) > >> --- >> Changelog: >> v3: >> Add Cc: stable@vger.kernel.org and pick up Barry's Reviewed-by. >> No code change compared to v2. >> Per the thread discussion, the __lru_gen_clear_refs() refactor will be >> sent as a separate cleanup after this fix lands. >> 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 35e242b48870b..ea3adb6a89d75 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); > Since you're not checking the return here, you could use > folio_set_lru_refs(folio, 0); > folio_clear_workingset(folio); Thanks for the review. That is exactly the shape we agreed on for the follow-up cleanup in this thread, Barry's __lru_gen_clear_refs() draft. I would still keep v3 as it is, for two reasons. folio_set_lru_refs() is only defined under CONFIG_LRU_GEN, so the open-coded version needs a new stub in mm_inline.h. That turns this one-spot fix into the header change we planned for the cleanup patch. The two calls are also unconditional, so on the classic LRU every lazyfree folio would lose PG_workingset too, which upstream never did before cc8ec7be78ff. Barry and Kairui just agreed to take this patch as a clean backport for stable, so that CLRU behaviour change should go into the cleanup patch with its own justification. lru_gen_clear_refs() is self-gated on gen >= 0, so the call is a no-op for folios that are not on a generation list, and the return value it computes shares the cacheline lruvec_del_folio() touches right after. I will send the cleanup, with the open-coded clearing and the stub in one place, once this lands. Best, Hui > >> 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 >> -- >> 2.43.0 >>