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=-7.0 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 B0B7EC54E4B for ; Tue, 12 May 2020 06:50:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 76A0720769 for ; Tue, 12 May 2020 06:50:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 76A0720769 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id F1260900098; Tue, 12 May 2020 02:50:53 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EC478900036; Tue, 12 May 2020 02:50:53 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DD905900098; Tue, 12 May 2020 02:50:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0104.hostedemail.com [216.40.44.104]) by kanga.kvack.org (Postfix) with ESMTP id C3C01900036 for ; Tue, 12 May 2020 02:50:53 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 807931EF3 for ; Tue, 12 May 2020 06:50:53 +0000 (UTC) X-FDA: 76807144386.28.tent41_24dc3c3141f19 X-HE-Tag: tent41_24dc3c3141f19 X-Filterd-Recvd-Size: 3598 Received: from mail-wr1-f65.google.com (mail-wr1-f65.google.com [209.85.221.65]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Tue, 12 May 2020 06:50:53 +0000 (UTC) Received: by mail-wr1-f65.google.com with SMTP id l11so7987066wru.0 for ; Mon, 11 May 2020 23:50:53 -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=k7eF3RNDZp8sEC0pL3FyWuKSdGUstddytrFYiZiZSn+NZxInPCSD8A16fOKF3ND+ut cmqn+bvGWMCELpTfYv9NXh9Itw/O0CIPMTrHdjahWzjSP1/vpP2AMkI4LODp+Dt7/FXY TxbbikZQCgorVkN7Uw0QyP/JHXCOY+cVIphKEtJ5NxltebI7kQlWX4jSJf+/HWAnzFIq DUJurVb1EKSDJMENUcChpg9StMq4/ZxBag5prYIUih75rOfFIusWjdPEVRxqVl+C0OvJ zGdQqjDUx8hFgUQ82W7m0eKANUcmjpRayv4snMZsm7NM69pZEXpS8wQNdIUUczEgCYXR E/wQ== X-Gm-Message-State: AOAM5334+k1FJs2nPMtmkt7dJvfQFX0v4dUrwmfDo5TYzjcu2UIujpst /G/32dGAoqZVfVQi93La/m8= 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> 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 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