From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 4359F2F8EAF for ; Fri, 17 Jul 2026 02:28:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784255304; cv=none; b=hd54p1koniRH3I0LSv0VES58vJ+5NY0PObXPQfH52FupO7jcQ5XHxAKBP7FRuolpUdhwBHf3vTTGvQe614jqvG9Mm7H9Uh68TnZa2bZeLOWKVsN/QY6hnpN42jPGk7i/yDwJWBJK4YD1BH9CCY0K8NIzX0ragbjNZbtpOekgNLw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784255304; c=relaxed/simple; bh=Ih5SLu2X4K5Fixk67XYx7zgqlcqgvqZxwoIRIrLPaqc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=DvS8wF9G8N9lAOBG3PqZ1SeAf5vqi8zPpL/TgxbLrrbpnMaL1jav0qPvq73wFZRomFO03QwckFoMykp6sZGRi4zMydBktugqWzea16j64ubq2TfvIDyc23WNR316qzP9+D/2OgJ36Dj1Ya8oV1aelPIjF1s904LtVhghWffqqIM= 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=VcWEPhq4; arc=none smtp.client-ip=95.215.58.174 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="VcWEPhq4" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784255289; 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=K7BquqktHv1/BZuLZY0RQng54+jc6Y0pgFNTnH/SVV0=; b=VcWEPhq4E+a+5McB+OTjqrvM3jg56G30RJxu5ay+P5eX+Y3Lf4/JaMWwS1D2For1jcDONU JqMi2TQAGD3a5C8HTdNvSIycx9sVWHReci4yRuvuItFztk+X5a2eu0QE/XVp2wApXo5L6z wArI5y4X5mCX4YMoBrH8kismyj4tVuY= Date: Fri, 17 Jul 2026 10:27:45 +0800 Precedence: bulk X-Mailing-List: cgroups@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> <94a489d5-8b02-46e6-92d2-ccb85f556769@linux.dev> <65305712-8598-46aa-822b-914298277b64@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <65305712-8598-46aa-822b-914298277b64@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 7/16/26 7:17 PM, Ridong Chen wrote: > > > On 7/16/2026 4:42 PM, Qi Zheng wrote: >> >> >> 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. >> > > Much better. > Would you mind if I send a separate patch to fix this issue? > Sure, thanks for your time on this, and I look forward to your fix!