From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) (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 5C9BD2DB794 for ; Sat, 18 Jul 2026 09:54:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784368453; cv=none; b=PDrVR/TnHyD/xQOj9EtOWnlTnPV+6khXCqRI9F2yMQlOjaFnRNJ7zY33XTH1Z5OiYcGmonv5Tsb1dOLpFExOPDnjzUGN1RwpPT0HUEkiSKKA5/JnaA4E2vQC0FIN71jywJafTN/O5G+L3RV7KthO6UZlKWpZ/4OQe0MVQC213kY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784368453; c=relaxed/simple; bh=6K+wru565EZSAc6eOSQX5rAMRLO603qn5um4ie3pkAk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Kev7yd8I0NLRxHzFaMyzD4GOvB+DV2t7zXiH0jCHSPem5sH7qs6lv9zGjoWE+BPx7XRQeHAk4Vsaax7gB+Awx52RCe9STWhw+fo93tBWels+HO+gCc8Yo5Prp54vmzrAg7x72ag4tfxpCfzw2YrSmPLeqF2o5r4jBI5XO7OgPyo= 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=IPZJ2vmv; arc=none smtp.client-ip=95.215.58.177 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="IPZJ2vmv" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784368450; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4Q+i8KecsNiTPDlAIDtRLOAH9MLCuFDqX7eHJi+IsDY=; b=IPZJ2vmvhKbB2s6jo0mwrZ5E3jVAfCVyiNyvZzuKXamWBoC2sL/Dj9CDm4Sxw640dP4ApZ imoYOnvUxNFjfm3w884NaHFRKH64hmv0sLPWe/uDiPo5CO9UmEjMtAQ+wt5Kr7siFL5IUz tFno2FMVgo8d4AbnwDd/uuNUw8x21go= From: Ridong Chen To: akpm@linux-foundation.org Cc: hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, ljs@kernel.org, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hezhongkun.hzk@bytedance.com, muchun.song@linux.dev, dave@stgolabs.net, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ridong.chen@linux.dev, Ridong Chen Subject: [PATCH v2 1/4] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max Date: Sat, 18 Jul 2026 17:52:48 +0800 Message-ID: <20260718095251.82937-2-ridong.chen@linux.dev> In-Reply-To: <20260718095251.82937-1-ridong.chen@linux.dev> References: <20260718095251.82937-1-ridong.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Ridong Chen As Qi mentioned [1], when swappiness=max (SWAPPINESS_ANON_ONLY) is set, the reclaim logic is expected to reclaim anonymous pages exclusively. However, due to the current ordering of checks in get_scan_count(), file pages may still be evicted if can_reclaim_anon_pages() returns false, which contradicts the semantics of SWAPPINESS_ANON_ONLY. Reproducer in a cgroup holding 64M of file cache, with no swap configured: Before (file cache is wrongly evicted): # cat memory.stat anon 196608 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim # cat memory.stat anon 208896 file 4096 <- page cache evicted pgsteal_proactive 16400 pgscan_proactive 16400 After (file cache is left intact): # cat memory.stat anon 200704 file 67178496 pgscan_proactive 0 # echo "64M swappiness=max" > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat memory.stat anon 208896 file 67178496 <- page cache untouched pgsteal_proactive 0 pgscan_proactive 0 Fix this by bailing out early when SWAPPINESS_ANON_ONLY is set and no anonymous pages are reclaimable, before falling back to file reclaim. [1] https://lore.kernel.org/cgroups/7ddf3eee-5fe2-45f7-8614-c8936a039e04@linux.dev/ Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim") Suggested-by: Qi Zheng Acked-by: Shakeel Butt Acked-by: Johannes Weiner Reviewed-by: Muchun Song Signed-off-by: Ridong Chen --- mm/vmscan.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96..d6b383d96a0c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2501,6 +2501,17 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, enum scan_balance scan_balance; enum lru_list lru; + /* Proactive reclaim initiated by userspace for anonymous memory only */ + if (swappiness == SWAPPINESS_ANON_ONLY) { + WARN_ON_ONCE(!sc->proactive); + if (!can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) { + memset(nr, 0, sizeof(*nr) * NR_LRU_LISTS); + return; + } + scan_balance = SCAN_ANON; + goto out; + } + /* 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; @@ -2519,13 +2530,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, 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; - } - /* * Do not apply any pressure balancing cleverness when the * system is close to OOM, scan both anon and file equally -- 2.43.0