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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50583C6FA82 for ; Mon, 12 Sep 2022 14:51:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C51C16B0071; Mon, 12 Sep 2022 10:51:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BFFB66B0073; Mon, 12 Sep 2022 10:51:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id AEEC68D0001; Mon, 12 Sep 2022 10:51:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id A13BB6B0071 for ; Mon, 12 Sep 2022 10:51:49 -0400 (EDT) Received: from smtpin01.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 767271A088B for ; Mon, 12 Sep 2022 14:51:49 +0000 (UTC) X-FDA: 79903722738.01.C0095A1 Received: from mail-pj1-f53.google.com (mail-pj1-f53.google.com [209.85.216.53]) by imf29.hostedemail.com (Postfix) with ESMTP id 195B71200CC for ; Mon, 12 Sep 2022 14:51:48 +0000 (UTC) Received: by mail-pj1-f53.google.com with SMTP id q62-20020a17090a17c400b00202a3497516so6079864pja.1 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=n+glf1tUDBPXPm8plfUDtcOIan7l/ft8Cy8jnDM3N0+OOXz63kf0WJWB77A3PUBVGe g04dYbcryRZ4U+DDG9mwxu+5ybW8+XrAeYTcQ2WYGucGDEaNbyINHodKpkJsl6DfNBCI 6Yqu9ZSaD77UgDG50fX5OEyKj43PIZyyyvSsAfJw8IJ0fVJ/iqxK5ee9Uz+p7Tb1HVvW HLeM1ZVrUMYLZMV9/nc9lCfsZHSjuAx6zzgtj0g+gAboc6GNnuWaqkVrCCXwgHxiEiZO 9j2vcco7kwx1KQq4Rf+94QwovarLGLsYnhQ1JZ+s2qksZueAzjXluzmDZ2md/YEtvlL/ t2wA== X-Gm-Message-State: ACgBeo2aVHX/KlSMW/HRyMxRdEHGE3E66vh7C8iIC1qIHiX/1KjBU2pu kNXhf8neerTo5cZdnChRUcxMtg== 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: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662994309; a=rsa-sha256; cv=none; b=iAGhbKsNBTtvpwMXfeIJbSQJA34HBAKZ5ccvnL/pHonsRY1zefjkv3vEP/LyRmsvk57v8Y sywT/vr7I6aOG6kOGzVnwb05l7tUMJFs3gcLeA85KyH4+YM86Mi11IU28WsUzR+wvYp0LP J5wRxnLqChREzLMSMnYWYbW4mS4uXT0= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="BN9Fko/7"; spf=pass (imf29.hostedemail.com: domain of senozhatsky@chromium.org designates 209.85.216.53 as permitted sender) smtp.mailfrom=senozhatsky@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662994309; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=LgLrA8w4lGgdiykWREg3/XrG7vTO7+v/5c4/2rZWRK8=; b=3e3BwLuCbtRX558uykE+kJD7PrTeskjQELKtA5BwPC3TJgjqxbdJI/qcNhM+F7n9s7A7Iz r5rz4A/DPTCOdSLxL/B078e8GddXO//XWBTCQhZAL0z8wW63XSNaiY0S2XFlgiY5X+uHQo Iu5gOvXkVCEtht0d/ugMlstcKZhMhrE= X-Rspamd-Queue-Id: 195B71200CC Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b="BN9Fko/7"; spf=pass (imf29.hostedemail.com: domain of senozhatsky@chromium.org designates 209.85.216.53 as permitted sender) smtp.mailfrom=senozhatsky@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 7nx88b1c9u5xyyzx5155zozd64x1b44w X-HE-Tag: 1662994308-240945 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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)