From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lgeamrelo07.lge.com (lgeamrelo07.lge.com [156.147.51.103]) (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 D95C63161A2 for ; Wed, 27 May 2026 06:23:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=156.147.51.103 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863034; cv=none; b=FUnULoQBzju/yg9C585zFeHkpa6v4mrwRu71uP2+n2PvhswLgTAb3Zq1/L+QKZ4A5RFYsqgFlgSLZCT0iF1MgTqHykLLHMzkjVbJ9ZPp8vHqj9aQ0BqOq8jtgD307jUplQeCWQUOfKaQES0N/YWxOEiOIjCBLXmcoYfD0MdsbX0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779863034; c=relaxed/simple; bh=oay6c+jrn56hkFby6pQILUHzTTGLnQOfn55wjDbY36M=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=DFPVAk884qkxQJfwCs43rh16FPFO/jarYHzIFQZjHLtoYzbL8c4h2kmNEdF2NDTbKekzhmXlfUeQpBo5Sk54B/V3fFqC6jgNbvUFv+Ipg4xoYtVr6vlcEeTWeAEOSH9FPdRdYHgK1wZGd227cAbzxORS5Uo4pU/+WvL30tKoj9o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com; spf=pass smtp.mailfrom=lge.com; arc=none smtp.client-ip=156.147.51.103 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lge.com Received: from unknown (HELO yjaykim-PowerEdge-T330.lge.net) (10.177.112.156) by 156.147.51.103 with ESMTP; 27 May 2026 15:23:50 +0900 X-Original-SENDERIP: 10.177.112.156 X-Original-MAILFROM: youngjun.park@lge.com From: Youngjun Park To: akpm@linux-foundation.org Cc: chrisl@kernel.org, youngjun.park@lge.com, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, mkoutny@suse.com, baver.bae@lge.com, matia.kim@lge.com Subject: [PATCH v7 4/4] mm: swap: filter swap allocation by memcg tier mask Date: Wed, 27 May 2026 15:22:47 +0900 Message-Id: <20260527062247.3440692-5-youngjun.park@lge.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260527062247.3440692-1-youngjun.park@lge.com> References: <20260527062247.3440692-1-youngjun.park@lge.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Apply memcg tier effective mask during swap slot allocation to enforce per-cgroup swap tier restrictions. In the fast path, check the percpu cached swap_info's tier_mask against the folio's effective mask. If it does not match, fall through to the slow path. In the slow path, skip swap devices whose tier_mask is not covered by the folio's effective mask. This works correctly when there is only one non-rotational device in the system and no devices share the same priority. However, there are known limitations: - When non-rotational devices are distributed across multiple tiers, and different memcgs are configured to use those distinct tiers, they may constantly overwrite the shared percpu swap cache. This cache thrashing leads to frequent fast path misses. - Combined with the above issue, if same-priority devices exist among them, a percpu cache miss (overwritten by another memcg) forces the allocator to round-robin to the next device prematurely, even if the current cluster is not fully exhausted. These edge cases do not affect the primary use case of directing swap traffic per cgroup. Further optimization is planned for future work. Signed-off-by: Youngjun Park --- mm/swapfile.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 9a86ebe992f4..1a2d29735b71 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1365,14 +1365,18 @@ static bool swap_alloc_fast(struct folio *folio) struct swap_cluster_info *ci; struct swap_info_struct *si; unsigned int offset; + int mask = folio_tier_effective_mask(folio); /* * Once allocated, swap_info_struct will never be completely freed, * so checking it's liveness by get_swap_device_info is enough. */ si = this_cpu_read(percpu_swap_cluster.si[order]); + if (!si || !swap_tiers_mask_test(si->tier_mask, mask)) + return false; + offset = this_cpu_read(percpu_swap_cluster.offset[order]); - if (!si || !offset || !get_swap_device_info(si)) + if (!offset || !get_swap_device_info(si)) return false; ci = swap_cluster_lock(si, offset); @@ -1392,10 +1396,14 @@ static bool swap_alloc_fast(struct folio *folio) static void swap_alloc_slow(struct folio *folio) { struct swap_info_struct *si, *next; + int mask = folio_tier_effective_mask(folio); spin_lock(&swap_avail_lock); start_over: plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) { + if (!swap_tiers_mask_test(si->tier_mask, mask)) + continue; + /* Rotate the device and switch to a new cluster */ plist_requeue(&si->avail_list, &swap_avail_head); spin_unlock(&swap_avail_lock); -- 2.34.1