From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 944AAECAAD5 for ; Mon, 12 Sep 2022 14:51:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230237AbiILOvv (ORCPT ); Mon, 12 Sep 2022 10:51:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39542 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230082AbiILOvt (ORCPT ); Mon, 12 Sep 2022 10:51:49 -0400 Received: from mail-pj1-x1036.google.com (mail-pj1-x1036.google.com [IPv6:2607:f8b0:4864:20::1036]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8605A1837C for ; Mon, 12 Sep 2022 07:51:48 -0700 (PDT) Received: by mail-pj1-x1036.google.com with SMTP id p1-20020a17090a2d8100b0020040a3f75eso8405789pjd.4 for ; Mon, 12 Sep 2022 07:51:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date; bh=LgLrA8w4lGgdiykWREg3/XrG7vTO7+v/5c4/2rZWRK8=; b=BN9Fko/7dUCTZ9hU/AQNESgmelgC6IuQ2JYDoDcxOsOI4M/AQUbxXNOIwHQrlqnEjX BEeSdDLBVX+RXncPsVDytvvUT74IzgXKGFi7EcM8Tc91HqWGOLOfJIBN5b2IS8C3KNDr 93CTgTluUZgdrwebpYtzfbXv4SJz+uanyyYhA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date; bh=LgLrA8w4lGgdiykWREg3/XrG7vTO7+v/5c4/2rZWRK8=; b=42YjWzG7pQVoQ47fZRKJx3vtsLKfH2nezIE/6glCRXoH9jiSdLVWFMP0XrS6clvhIR fiZj7xSJj8bcO1NKAPZSdR3dbM44NH1OvI2PKeXaefSxWESTCOAYBmknaNzinky3blIe IuydVQNxk3o+vnh8o2H07+J/QvVlGIJGPliuHf5FTrcokxWwPW7l8x02S/mUBN4yPT7N 9wMscdlCUI61Kryy23pSk8HrjnkgrdsEtX353Y/3jg+Fi+5c3ZJ7VJKwx/TFM6XB9e6y Y8kCWNLb+90v6ACDCJF3fJVWH+RYL+5JJ1CMJ0T2nZrOUWP7ZjcsrKayB4BRJ6b1SI4G +N6Q== X-Gm-Message-State: ACgBeo1SuFiTcSVB1sWLFNln9NmdP4SuIQRXMD+yWZ+1yzDoN3TEsI2C qLGXm6jt3a95OiZxQ4E3vJczag== X-Google-Smtp-Source: AA6agR5b/y7dalrpDcvsskkc5HQXP7heua38BHRB+7iUY+5gwN7ebjn5H1kofu5KiUED5Cn7EQxgtw== X-Received: by 2002:a17:902:f541:b0:176:e8f1:cd57 with SMTP id h1-20020a170902f54100b00176e8f1cd57mr25894799plf.8.1662994308064; Mon, 12 Sep 2022 07:51:48 -0700 (PDT) Received: from google.com ([240f:75:7537:3187:481a:bead:f512:e554]) by smtp.gmail.com with ESMTPSA id m20-20020a170902c45400b0016d72804664sm6032114plm.205.2022.09.12.07.51.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Sep 2022 07:51:47 -0700 (PDT) Date: Mon, 12 Sep 2022 23:51:42 +0900 From: Sergey Senozhatsky To: Brian Geffon , Minchan Kim Cc: Andrew Morton , Nitin Gupta , LKML , linux-mm , Sergey Senozhatsky Subject: Re: [PATCH] zram: do not waste zram_table_entry flags bits Message-ID: References: <20220912053755.156704-1-senozhatsky@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (22/09/12 23:37), Sergey Senozhatsky wrote: > > > -#define ZRAM_FLAG_SHIFT 24 > > > +#define ZRAM_FLAG_SHIFT (PAGE_SHIFT + 1) > > > > Why not just hard code 16 with an explanation that it cannot be > > increased further using the analysis you did in the other thread? It's > > going to be tricky to reason about how many free flag bits actually > > remain with PAGE_SHIFT across all architectures, especially given we > > have no architecture specific flags. > > Well, zram should not make any assumptions on arch code. How do > we know that PAGE_SHIFT 16 is the max value we will ever have? > Some arch can come around someday and use PAGE_SHIFT say, 18, > and we won't be aware of it (using hardcoded value of 16) until > someone hits a really hard to debug problem in zram. And I'd probably also add something like this, to keep us alert should we run out of bits in the future: --- diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index f3948abce2f7..07913bcdb5c2 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -2449,6 +2449,8 @@ static int __init zram_init(void) { int ret; + BUILD_BUG_ON(__NR_ZRAM_PAGEFLAGS > BITS_PER_LONG); + ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare", zcomp_cpu_up_prepare, zcomp_cpu_dead); if (ret < 0)