From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta1.migadu.com (out-189.mta1.migadu.com [95.215.58.189]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C132D3E2756 for ; Thu, 16 Jul 2026 08:43:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784191385; cv=none; b=NNbs/Rpjr+1AER/o2u5LdaXix8oxyWx5nFxFua50pEtQnaTcuZcChPBEMJ9A5bv8S57hkpFeAOYsVOIzK5Fq8UoG2zSTkNgnFuVBJbcJ++fSQiLNfaoB+Dm0+CcIm10NJPoYbnY6GelaUvbJ7y8WA1/6Gezd/lumrQNCiz56nVo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784191385; c=relaxed/simple; bh=go62PKRAlcngrK1Hy0d7dPJaDh5wBjvRpRw0Lx3Gbq4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=k/V9mNX/4bcigBvAdlOQp+AgVtsAz9OYfERlIbRJoc7b06yzhgtNGgmHhlvKURnhIfah4u9XhNGErt7fYwBvdMK7Unm9TUdhX0wzXDXLpmfDHbwAiU+ZGAQZAqTpuGIyd7LVxsO3GnmyRU3t10JtAdqVYp3JfDCe8bC6Ce0UxQA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=gQ3/hoSc; arc=none smtp.client-ip=95.215.58.189 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) header.d=linux.dev header.i=@linux.dev header.b="gQ3/hoSc" Message-ID: <94a489d5-8b02-46e6-92d2-ccb85f556769@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784191371; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Ja9q5YNM9G+iFAQ4USLdAyYzPDLR1TKQogJvW0VZQhg=; b=gQ3/hoScl6UK3GoY+N/bQG+67l3bmhmL1Bu73KB0SK98rScna6iegHEOyxCAobOWPRp0vl r9XMlh+lrfrHBX3IwPMY/80WidicA+JoNTkRjG3o6WJG/xfJEDVCdX7YNdhI+5v7gOHgnC 1xOcO1CsfHEPGM9ptUkYleVd1P/90i8= Date: Thu, 16 Jul 2026 16:42:31 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter To: Ridong Chen , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton , Chris Li , Kairui Song Cc: Muchun Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Youngjun Park , David Hildenbrand , Lorenzo Stoakes , Axel Rasmussen , Yuanchu Xie , Wei Xu , Davidlohr Bueso , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ridong Chen , stable@vger.kernel.org References: <20260716031729.1064007-1-ridong.chen@linux.dev> <20260716031729.1064007-3-ridong.chen@linux.dev> <7ddf3eee-5fe2-45f7-8614-c8936a039e04@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 7/16/26 4:21 PM, Ridong Chen wrote: > > > On 7/16/2026 11:58 AM, Qi Zheng wrote: >> Hi Ridong, >> >> On 7/16/26 11:17 AM, Ridong wrote: >>> From: Ridong Chen >>> >>> sc_swappiness() had two separate definitions depending on >>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned >>> vm_swappiness, ignoring the proactive_swappiness value passed >>> through scan_control. This caused the swappiness parameter >>> written to /sys/devices/system/node/nodeX/reclaim to have no >>> effect when CONFIG_MEMCG is disabled. >>> >>> Fix this by consolidating sc_swappiness() into a single definition >>> that checks sc->proactive_swappiness first, then falls back to >>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG >>> and !CONFIG_MEMCG. >>> >>> Before fix (swappiness=max ignored, mostly file pages reclaimed): >>> >>>      # cat /proc/sys/vm/swappiness >>>      60 >>>      # cat /proc/vmstat | grep pgsteal >>>      pgsteal_kswapd 0 >>>      pgsteal_direct 0 >>>      pgsteal_khugepaged 0 >>>      pgsteal_proactive 1840 >>>      pgsteal_anon 25 >>>      pgsteal_file 1815 >>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/ >>> reclaim >>>      # cat /proc/vmstat | grep pgsteal >>>      pgsteal_kswapd 0 >>>      pgsteal_direct 0 >>>      pgsteal_khugepaged 0 >>>      pgsteal_proactive 18013 >>>      pgsteal_anon 337 >>>      pgsteal_file 17676 >>> >>> After fix (swappiness=max honored, anon pages reclaimed as expected): >>> >> >> By the way, in get_scan_count(), it seems we still reclaim file pages >> without swap space, even if swappiness=max (SWAPPINESS_ANON_ONLY) is >> set. >> >> This behavior appears to contradict the semantics of >> SWAPPINESS_ANON_ONLY, which probably needs a fix as well. >> > Thanks, Qi. > > You're right. Currently, when can_reclaim_anon_pages() returns false, > the reclaim logic falls back to scanning file folios even if swappiness > == SWAPPINESS_ANON_ONLY is set: > > ``` > static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, >                unsigned long *nr) > { >     .... >     /* If we have no swap space, do not bother scanning anon folios. */ >     if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, > sc)) { >         scan_balance = SCAN_FILE; >         goto out; >     } > >     ... >     /* Proactive reclaim initiated by userspace for anonymous memory > only */ >     if (swappiness == SWAPPINESS_ANON_ONLY) { >         WARN_ON_ONCE(!sc->proactive); >         scan_balance = SCAN_ANON; >         goto out; >     } >     ... > } > ``` > > The !can_reclaim_anon_pages() check above takes precedence over the > SWAPPINESS_ANON_ONLY branch, making the latter effectively unreachable > when anonymous pages are deemed non-reclaimable. > > To fix this, could we move the SWAPPINESS_ANON_ONLY check up before the > can_reclaim_anon_pages() check? > > ``` > static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, >                unsigned long *nr) > { >     ... >     /* Proactive reclaim initiated by userspace for anonymous memory > only */ >     if (swappiness == SWAPPINESS_ANON_ONLY) { >         WARN_ON_ONCE(!sc->proactive); >         scan_balance = SCAN_ANON; >         goto out; For SWAPPINESS_ANON_ONLY + !can_reclaim_anon_pages, perhaps we should just return directly instead of goto out, since no pages can be reclaimed in this situation. Thanks, Qi >     } >     .... >     /* If we have no swap space, do not bother scanning anon folios. */ >     if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, > sc)) { >         scan_balance = SCAN_FILE; >         goto out; >     } > >     ... > } > ``` >