From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (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 D6424392828 for ; Thu, 16 Jul 2026 11:17:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784200652; cv=none; b=jBm/d7fNf1evjcHyEc02bMnL3d+a0/Z8o1OwvQ/rdWhP6Bu9CpJvagh6F1eP3+FsWNpsfyD2VNk7KLZw+rhGrhuElLQzHVBQZiL1deyF5hwR7SAhqLhQ6dm7yLZFaq+/eu3Bt4lRoh/O1aVVQyaUsHhk5jML/lrtHYKE0Ecagls= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784200652; c=relaxed/simple; bh=7kl6bwyaVgSrLTnoWraAKy7A1ORdxO4LmRRsCznSOU4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=q5AJS6r+tRa3TJYYOW0xHKhDeq0Kls91gOgDHiYLztmiSfR75PDuLrXurKK88P50Fo2sAEpyFy2nu+yXKovHPS0xzvPoZCcH5OKpsB/88sGihF5mMA2hzQQgiJxNqCLZ0VLfq1b15vnoT9dfVcQTCtjkMM7mLe/qB+rMDVZsF2c= 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=iw2ftw/N; arc=none smtp.client-ip=91.218.175.178 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="iw2ftw/N" Message-ID: <65305712-8598-46aa-822b-914298277b64@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784200638; 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=hTG6hGzVl0dWfit8w/MB62E4ZbeaEHmlylI6bepXRC8=; b=iw2ftw/NK2C6aLDREmrqRB3OjKsp0m0NcDAUexkCvaS+1CoWYFdLyp3g94WH+U7yxEgSiM lGZoR+GtGUfnBlAM39TYcBixAEmtd9mi5XewkykQWHEgkw7LVMayH0akxk3gu2SaXH9Sp5 w0xjNbEHkRdLLMISoubCAbwZcP3ZMYQ= Date: Thu, 16 Jul 2026 19:17:03 +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: Qi Zheng , 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ridong Chen In-Reply-To: <94a489d5-8b02-46e6-92d2-ccb85f556769@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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? > >>      } >>      .... >>      /* 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; >>      } >> >>      ... >> } >> ``` >> > -- Best regards Ridong