From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (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 51B4F3812DA for ; Thu, 23 Jul 2026 04:57:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784782678; cv=none; b=gxjO7ivm2+7Vlj7YlaYkO/U3vdE34/a+40HcjXnzhxpkQpYMRJPlSPkPLlyQIUnnwcbcftMCIGFdVJXJnYqu4GyopBZHw8VHtY5eXePCSlfP6z6NzaP3zMOlq75DKO+vqazinfojtNfssQQ5rBLEm0qPWfrs1gv123cwIZNd6Kw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784782678; c=relaxed/simple; bh=nopkLGQjxyCvDc5NWUmj3PpMHMg9QQc4M01a5XIRBgc=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=cbDgglgMxj8eMm2xo104OROW9BcrsjaoJeHo+2ZImif6MXhiqDYgbIsfzQuf5332/gyz0+f82fX0H09nhwqmWp2qYxnXPvT5GfpSTs8Cu69OeFuKRpF8wrssGCeq3rjRYO6ml+MNGC7eOamj2TvJ19X0uX708n9LUeRP15EGxPo= 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=PVYGstw7; arc=none smtp.client-ip=91.218.175.171 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="PVYGstw7" 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=1784782666; 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=+M31gX24/lXdo/71mKqeb9yMjPYP0lhEdBSZm1x7d2Y=; b=PVYGstw7O1AshQlF7Vggr7tyf7t6fBgn/m1/RtemzMXcw63/0ICwW4qp8tqDCErm59X7+q WMgJrDtEtc6OS2rQPuc/BSRn45sRy+z+XeiJwIiDqGsX72W0torSudl1fHn/gkEzoM1upD uzVrvWaG2LLwEZoO5GDLy4Wz2EAlZ+Y= From: Ridong To: Andrew Morton , Johannes Weiner Cc: David Hildenbrand , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Zhongkun He , Muchun Song , Davidlohr Bueso , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ridong Chen , Ridong Chen Subject: [PATCH v3 1/4] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max Date: Thu, 23 Jul 2026 12:57:15 +0800 Message-Id: <20260723045718.2052070-2-ridong.chen@linux.dev> In-Reply-To: <20260723045718.2052070-1-ridong.chen@linux.dev> References: <20260723045718.2052070-1-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 Reviewed-by: Qi Zheng Reviewed-by: Barry Song Signed-off-by: Ridong Chen --- mm/vmscan.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96..2c689682b952 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2501,6 +2501,23 @@ 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. + * SWAPPINESS_ANON_ONLY is set only on the proactive reclaim path, so + * warn if it shows up elsewhere. When anon cannot be reclaimed (e.g. + * no swap), bail out instead of falling back to evicting file pages, + * which would violate the anon-only semantics. + */ + 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 +2536,6 @@ 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 -- 2.34.1