From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (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 A762238DD2 for ; Fri, 6 Sep 2024 02:24:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725589457; cv=none; b=RxQKkn+SqSTtGbm/QTf/c7Sz875WONfxtYIJTGHa3ELQXZT9/cC64wk8K96ufZOcb1eSKOfJBEugNAyyHuuI42g+BRiuoDCKoggRh/GFSTJFAeJR7xYcqY8x6+LaGtV0Lxk4KywBByzR7mHIO7YDeeJJY7oDaXdS1BHwDCEFgvo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725589457; c=relaxed/simple; bh=yOjmIXa4emd5ltyBCbc6RJMJvvbRw+EgmqF8MEJr/1E=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=vBfC7mVHzPS9X83Y9L7Bpd20Vbv1JIoVsfO91ft0OdBBvo2lHBn6JH3evaAVDZoDUvVyowLoQluZN/BKjZI0HLW7XL2oDwVnDtFBc1sM17eaNpULM+0NOOF0us6H7WICs+gzeqVn0RKcaePrYkcKZlvhqsaQB5O4UmtyQwhxAWk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.194]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4X0KkK2RxczpVSm; Fri, 6 Sep 2024 10:22:17 +0800 (CST) Received: from kwepemd200019.china.huawei.com (unknown [7.221.188.193]) by mail.maildlp.com (Postfix) with ESMTPS id 790B81400DC; Fri, 6 Sep 2024 10:24:12 +0800 (CST) Received: from [10.173.127.72] (10.173.127.72) by kwepemd200019.china.huawei.com (7.221.188.193) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Fri, 6 Sep 2024 10:24:11 +0800 Subject: Re: [PATCH v2] mm: z3fold: deprecate CONFIG_Z3FOLD To: Yosry Ahmed , Andrew Morton CC: Vitaly Wool , Johannes Weiner , Nhat Pham , Huacai Chen , WANG Xuerui , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Aneesh Kumar K.V , "Naveen N. Rao" , Christoph Hellwig , Sergey Senozhatsky , Chris Down , , , , References: <20240904233343.933462-1-yosryahmed@google.com> From: Miaohe Lin Message-ID: <1d3a5751-8af7-8ca9-8dff-4de2597f9751@huawei.com> Date: Fri, 6 Sep 2024 10:24:10 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20240904233343.933462-1-yosryahmed@google.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemd200019.china.huawei.com (7.221.188.193) On 2024/9/5 7:33, Yosry Ahmed wrote: > The z3fold compressed pages allocator is rarely used, most users use > zsmalloc. The only disadvantage of zsmalloc in comparison is the > dependency on MMU, and zbud is a more common option for !MMU as it was > the default zswap allocator for a long time. > > Historically, zsmalloc had worse latency than zbud and z3fold but > offered better memory savings. This is no longer the case as shown by > a simple recent analysis [1]. That analysis showed that z3fold does not > have any advantage over zsmalloc or zbud considering both performance > and memory usage. In a kernel build test on tmpfs in a limited cgroup, > z3fold took 3% more time and used 1.8% more memory. The latency of > zswap_load() was 7% higher, and that of zswap_store() was 10% higher. > Zsmalloc is better in all metrics. > > Moreover, z3fold apparently has latent bugs, which was made noticeable > by a recent soft lockup bug report with z3fold [2]. Switching to > zsmalloc not only fixed the problem, but also reduced the swap usage > from 6~8G to 1~2G. Other users have also reported being bitten by > mistakenly enabling z3fold. > > Other than hurting users, z3fold is repeatedly causing wasted > engineering effort. Apart from investigating the above bug, it came up > in multiple development discussions (e.g. [3]) as something we need to > handle, when there aren't any legit users (at least not intentionally). > > The natural course of action is to deprecate z3fold, and remove in a few > cycles if no objections are raised from active users. Next on the list > should be zbud, as it offers marginal latency gains at the cost of huge > memory waste when compared to zsmalloc. That one will need to wait until > zsmalloc does not depend on MMU. > > Rename the user-visible config option from CONFIG_Z3FOLD to > CONFIG_Z3FOLD_DEPRECATED so that users with CONFIG_Z3FOLD=y get a new > prompt with explanation during make oldconfig. Also, remove > CONFIG_Z3FOLD=y from defconfigs. > > [1]https://lore.kernel.org/lkml/CAJD7tkbRF6od-2x_L8-A1QL3=2Ww13sCj4S3i4bNndqF+3+_Vg@mail.gmail.com/ > [2]https://lore.kernel.org/lkml/EF0ABD3E-A239-4111-A8AB-5C442E759CF3@gmail.com/ > [3]https://lore.kernel.org/lkml/CAJD7tkbnmeVugfunffSovJf9FAgy9rhBVt_tx=nxUveLUfqVsA@mail.gmail.com/ > > Acked-by: Chris Down > Acked-by: Nhat Pham > Signed-off-by: Yosry Ahmed LGTM. Thanks for your patch. Reviewed-by: Miaohe Lin Thanks. .