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 X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45B31C54E8D for ; Tue, 12 May 2020 06:50:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2225C20769 for ; Tue, 12 May 2020 06:50:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589266255; bh=YoY5axcAKndaHvfi5URiqrWyh4PRHWdm8XpDzzV9a6g=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=XjR0j2iBdcWXP/MIC9g+eIQLXBwg022LKj6hlxqxfkLbnWfoyFtk4ZXWUkTrVkm5t ajDPUMICoofazom574ILdUxYNuAqQLF3U6UNI+T33rr4cFNqzBYEG47CKufhWKj4v1 xUBCxgAL5u014b1zzeextiEF8qPj3cH0tRY+LKNg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728947AbgELGuy (ORCPT ); Tue, 12 May 2020 02:50:54 -0400 Received: from mail-wr1-f66.google.com ([209.85.221.66]:47027 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727783AbgELGuy (ORCPT ); Tue, 12 May 2020 02:50:54 -0400 Received: by mail-wr1-f66.google.com with SMTP id w7so13900762wre.13 for ; Mon, 11 May 2020 23:50:52 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=+XD8Y6tEmtTs7vMbjo81XnVFNhe7jSdvdt/s8YEjaHg=; b=fJ4NgJBitmlM4bWZgBKXY58JYV0LpHe72G28608gKXHv42HNY2LvuVq49YBxk8JuZy UxOEfglC3y9j6CcG7D3nAK0APAVtkzUdIWHhhssRIAPyLVHv6J0K8nIb9uNiyWzoxZ7Q OpkjVyST//lR8b0p+8kSGUg8dnlBriM3ckIRyTAUyfXC7r6J9C3Y+tY5+LAHLKPxc5Kh YD/37Agqr16mVAjaCDu1E1u5nRMf+29WzhgDUdc305w8bRhtCYKYPaGIosoTUJVM3NfR lWhIkjPe5qoKpiA58MPUGL2XFHrqQB2z/lC0FmHPriL87ssXLzAMHrFjOH7r18r/v15n usaA== X-Gm-Message-State: AOAM532ldc29Qtt9581utA0brE3Yo/XtyhUE1U2r4jW0518OqqJKR1Xe khOZF+js2OO5ACJaPHSZCRQ= X-Google-Smtp-Source: ABdhPJyFGZYUUdE1D+dABJILUqbs/VUgmZJNuPKdPWmELcviQhZMyMcGBy49OvSxvATewfewlQBtvQ== X-Received: by 2002:a05:6000:1187:: with SMTP id g7mr961988wrx.54.1589266252064; Mon, 11 May 2020 23:50:52 -0700 (PDT) Received: from localhost (ip-37-188-140-86.eurotel.cz. [37.188.140.86]) by smtp.gmail.com with ESMTPSA id 81sm13287230wme.16.2020.05.11.23.50.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 11 May 2020 23:50:50 -0700 (PDT) Date: Tue, 12 May 2020 08:50:49 +0200 From: Michal Hocko To: Huang Ying Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Minchan Kim , Tim Chen , Hugh Dickins Subject: Re: [PATCH] mm, swap: Use prandom_u32_max() Message-ID: <20200512065049.GN29153@dhcp22.suse.cz> References: <20200512064147.514493-1-ying.huang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200512064147.514493-1-ying.huang@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 12-05-20 14:41:46, Huang Ying wrote: > To improve the code readability and get random number with higher > quality. I understand the readability argument but why should prandom_u32_max (which I was not aware of) provide a higher quality randomness? > Signed-off-by: "Huang, Ying" > Cc: Michal Hocko > Cc: Minchan Kim > Cc: Tim Chen > Cc: Hugh Dickins To the change itself Acked-by: Michal Hocko > --- > mm/swapfile.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index a0a123e59ce6..2ec8b21201d6 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -3220,7 +3220,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) > * select a random position to start with to help wear leveling > * SSD > */ > - p->cluster_next = 1 + (prandom_u32() % p->highest_bit); > + p->cluster_next = 1 + prandom_u32_max(p->highest_bit); > nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER); > > cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info), > -- > 2.26.2 -- Michal Hocko SUSE Labs