From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lgeamrelo03.lge.com (lgeamrelo03.lge.com [156.147.51.102]) (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 EA3E235838B for ; Sat, 18 Apr 2026 12:27:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=156.147.51.102 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776515256; cv=none; b=OKu9x5wsMMgkd/nQ4rxlN3VsRox02Hp4EquIsZPcFN4ZVzQxl+hIfphYEWYxjpkuV8XK7k6HnoEnR5f9Yl/y7vu4/RvSHbuEyFtZhR8++CqZeov5+/j1ol0r9kEZuvx62Uzn8fHcaswAAXxgeh1H2jv19w4t1ixCgPDl0X07mMQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776515256; c=relaxed/simple; bh=789KyVGeT3sgUL0ELlTj+p02bnEamtRqykKebIxryAo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mF8HtYhWLc45K3XDpDsvwsvSElafPuhqkWEL4vBpjPDr1rS5zKYIXbwbN9QKSLokVPx2kRZS/dALX8r54Zdz68VIK+rxp5j37nRm1k1YzSeK4aNsJSD81Kzwd+do8iTh8+0sbA/o6m+ay1w3K9ByoO875m2w0+4Vu88EBAVfwaA= 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=156.147.51.102 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) (10.177.112.156) by 156.147.51.102 with ESMTP; 18 Apr 2026 21:27:23 +0900 X-Original-SENDERIP: 10.177.112.156 X-Original-MAILFROM: youngjun.park@lge.com Date: Sat, 18 Apr 2026 21:27:23 +0900 From: YoungJun Park To: kasong@tencent.com Cc: linux-mm@kvack.org, Andrew Morton , David Hildenbrand , Zi Yan , Baolin Wang , Barry Song , Hugh Dickins , Chris Li , Kemeng Shi , Nhat Pham , Baoquan He , Johannes Weiner , Chengming Zhou , Roman Gushchin , Shakeel Butt , Muchun Song , Qi Zheng , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Yosry Ahmed , Lorenzo Stoakes , Dev Jain , Lance Yang , Michal Hocko , Michal Hocko , Qi Zheng Subject: Re: [PATCH v2 11/11] mm, swap: merge zeromap into swap table Message-ID: References: <20260417-swap-table-p4-v2-0-17f5d1015428@tencent.com> <20260417-swap-table-p4-v2-11-17f5d1015428@tencent.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260417-swap-table-p4-v2-11-17f5d1015428@tencent.com> On Fri, Apr 17, 2026 at 02:34:41AM +0800, Kairui Song via B4 Relay wrote: > * > * Usages: > * > @@ -74,17 +76,22 @@ struct swap_memcg_table { > #define SWP_TB_PFN_MARK_BITS 2 > #define SWP_TB_PFN_MARK_MASK (BIT(SWP_TB_PFN_MARK_BITS) - 1) > > -/* SWAP_COUNT part for PFN or shadow, the width can be shrunk or extended */ > -#define SWP_TB_COUNT_BITS min(4, BITS_PER_LONG - SWP_TB_PFN_BITS) > +/* SWAP_COUNT and flags for PFN or shadow, width can be shrunk or extended */ > +#define SWP_TB_FLAGS_BITS min(5, BITS_PER_LONG - SWP_TB_PFN_BITS) > +#define SWP_TB_COUNT_BITS (SWP_TB_FLAGS_BITS - 1) Hi Kairui :) Would this break the build on 32-bit arches with 40-bit phys addrs (MAX_POSSIBLE_PHYSMEM_BITS = 40)? Architectures I checked. - ARM LPAE (CONFIG_ARM_LPAE=y) - ARC PAE40 (CONFIG_ARC_HAS_PAE40=y) - MIPS XPA (CONFIG_XPA=y) Calculations. SWP_TB_PFN_BITS = 28 + 2 = 30 SWP_TB_FLAGS_BITS = min(5, 32 - 30) = 2 SWP_TB_COUNT_BITS = 2 - 1 = 1 The BUILD_BUG_ON looks like the real problem. it needs at least 3 count values (free/used/overflow). BUILD_BUG_ON(SWP_TB_COUNT_MAX < 2 || SWP_TB_COUNT_BITS < 2); Confirmed with a cross build (multi_v7_defconfig + lpae.config). error: BUILD_BUG_ON failed: SWP_TB_COUNT_MAX < 2 || SWP_TB_COUNT_BITS < 2 at __count_to_swp_tb (mm/swap_table.h:227) I think the right fix is widening swap_tb to 64 bits unconditionally (atomic64_t). (Or, uglier, these arches could always route counts through the extend table.) Best regards, Youngjun Park