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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 55650C3404C for ; Thu, 20 Feb 2020 05:13:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2DB862465D for ; Thu, 20 Feb 2020 05:13:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="SjzIXiSS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728073AbgBTFNC (ORCPT ); Thu, 20 Feb 2020 00:13:02 -0500 Received: from mail27.static.mailgun.info ([104.130.122.27]:34662 "EHLO mail27.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725957AbgBTFNB (ORCPT ); Thu, 20 Feb 2020 00:13:01 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1582175581; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=Ao1uwixRp+mRr4IVPkNGuxraZYvp+rb//Bou7aXajek=; b=SjzIXiSSBhskYb4oNvCHmSzBmyzNbOFVXBAsMnW3OdKYT2dwR66oIwdRaHnCmuNlQjomVXCG PGiAtUyxnrfTuRGWXYVXknFGR/7r60rsDXalrEyqKwD6pcuOCENUktpeX7ffSNXdppChPfL2 i5rA2/q5YKw/dQTVyP6spg9zFUg= X-Mailgun-Sending-Ip: 104.130.122.27 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5e4e1556.7fad6d94e848-smtp-out-n01; Thu, 20 Feb 2020 05:12:54 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 1EA5CC4479F; Thu, 20 Feb 2020 05:12:53 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: vjitta) by smtp.codeaurora.org (Postfix) with ESMTPSA id 11D60C43383; Thu, 20 Feb 2020 05:12:52 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 20 Feb 2020 10:42:52 +0530 From: vjitta@codeaurora.org To: Christopher Lameter Cc: penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, vinmenon@codeaurora.org, kernel-team@android.com, linux-kernel-owner@vger.kernel.org Subject: Re: [PATCH] mm: slub: reinitialize random sequence cache on slab object update In-Reply-To: <7bf56496-7b8a-c60f-b261-9505068f9130@codeaurora.org> References: <1580379523-32272-1-git-send-email-vjitta@codeaurora.org> <7bf56496-7b8a-c60f-b261-9505068f9130@codeaurora.org> Message-ID: X-Sender: vjitta@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-02-03 12:27, Vijayanand Jitta wrote: > On 1/30/2020 11:58 PM, Christopher Lameter wrote: >> On Thu, 30 Jan 2020, vjitta@codeaurora.org wrote: >> >>> Random sequence cache is precomputed during slab object creation >>> based up on the object size and no of objects per slab. These could >>> be changed when flags like SLAB_STORE_USER, SLAB_POISON are updated >>> from sysfs. So when shuffle_freelist is called during slab_alloc it >> >> Sorry no. That cannot happen. Changing the size of the slab is only >> possible if no slab pages are allocated. Any sysfs changes that affect >> the >> object size must fail if object and slab pages are already allocated. >> >> If you were able to change the object size then we need to prevent >> that >> from happening. >> > > Yes, size of slab can't be changed after objects are allocated, that > holds > true even with this change. Let me explain a bit more about the use > case here > > ZRAM compression uses the slub allocator, by enabling the slub debug > flags like > SLAB_STORE_USER etc.. the memory consumption will rather be increased > which doesn't > serve the purpose of ZRAM compression. So, such flags are to be > disabled before the > allocations happen, this requires updation of random sequence cache as > object > size and number of objects change after these flags are disabled. > > So, the sequence will be > > 1. Slab creation (this will set a precomputed random sequence cache) > 2. Remove the debug flags > 3. update the random sequence cache > 4. Mount zram and then start using it for allocations. > > Thanks, > Vijay Waiting for your response. Thanks, Vijay