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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 6ED2DC43441 for ; Thu, 22 Nov 2018 06:59:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2E9C520864 for ; Thu, 22 Nov 2018 06:59:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ej2i4XMB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2E9C520864 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392334AbeKVRhf (ORCPT ); Thu, 22 Nov 2018 12:37:35 -0500 Received: from mail-pg1-f195.google.com ([209.85.215.195]:46301 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732578AbeKVRhf (ORCPT ); Thu, 22 Nov 2018 12:37:35 -0500 Received: by mail-pg1-f195.google.com with SMTP id w7so1270166pgp.13 for ; Wed, 21 Nov 2018 22:59:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=tXk/Ip4jQz/WKT17CfBtE3AcIWzJODmjTMo36/daKds=; b=ej2i4XMBRxZh3SDJnbjRLaLHwS3RbD/KneT4jGu47TABfZVLGlUVbHsNlrGQ4krv09 YxDlJM8f2B9ketHgDRcbOBYeXY1wn4zYiC2Bz9Nya/QdHyiIq6jBjIIDxETLr5riUUde MnQurt4XN+i5Flc67nKq/U1nU7xoPZTqlS88/2H8XTQo6oxg/azqzMLoVPB8IS4ZTP/q UNITjItaBvc0A+q+uOwF6o4nXXaFSKelDEEdfRB/ydFRdIbqqQToWI0IW3nS4QbK5bfX uqKNw9uhcjyS71nqF96iOJfY1Mkwn65s5vfr9dmYPnKt5nmNSOkjDRY4jMXeRt+dWuwO /srw== 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:user-agent; bh=tXk/Ip4jQz/WKT17CfBtE3AcIWzJODmjTMo36/daKds=; b=KyrV7jU1evtnJfN1KWEK+km6lRhY0+Ptcaze57uJg0DHTDkCoGTIMg/Dr0rVLOdGuA xO2gi2JMrFce85AZvtDO4gFbQQ/vRcWwa96E4n1BL45cH03vMyK1cIzdId1+OjGMnz1v TPOuXbEMuftu9yOoqJOSxGt1ZIeMtuQ/6T3ODrni+Uuo78tpxBFq4dL1dXRL3q1hVRGo 2iYlrgGX+yMfaBT0aNOOjtAsUofvKA1Dw+jkogbcjqxKCKAQ44FwtUerFsp8wjkn8vjE GylI4NI/s0TbQ6mX4Zym5AFWxg4uqssbPP+U+ssw/Y5Gr+VmMzcPpsuMN0Tj43pQBdgg BZZw== X-Gm-Message-State: AA+aEWbXvI8D6bSM9/mm11/TRJ0/VezepHUxCquOBUM8Ah5Akr/7RLpY 7v126jWHJN+T+uX8R+mPyBs= X-Google-Smtp-Source: AFSGD/WvEo+YoAQCUaqltEcrTtjuv+7JSE6mSpx1gwezrb3G6uERlA/ySezIT+2areyPvLvTnRMw6A== X-Received: by 2002:a63:507:: with SMTP id 7mr5802218pgf.411.1542869971344; Wed, 21 Nov 2018 22:59:31 -0800 (PST) Received: from localhost ([175.223.27.1]) by smtp.gmail.com with ESMTPSA id 5-v6sm57369963pfg.141.2018.11.21.22.59.29 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 21 Nov 2018 22:59:30 -0800 (PST) Date: Thu, 22 Nov 2018 15:59:26 +0900 From: Sergey Senozhatsky To: Minchan Kim Cc: Sergey Senozhatsky , Andrew Morton , LKML Subject: Re: [PATCH 4/6] zram: support idle page writeback Message-ID: <20181122065926.GG3441@jagdpanzerIV> References: <20181116072035.155108-1-minchan@kernel.org> <20181116072035.155108-5-minchan@kernel.org> <20181121045551.GC599@jagdpanzerIV> <20181121133408.GA103278@google.com> <20181122021442.GB3441@jagdpanzerIV> <20181122050437.GA182024@google.com> <20181122054040.GE3441@jagdpanzerIV> <20181122061542.GA211816@google.com> <20181122063103.GB211816@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181122063103.GB211816@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (11/22/18 15:31), Minchan Kim wrote: > > > > I got what you mean now. Let's call it as "incompressible page wrieback" > > to prevent confusing. > > > > "incompressible page writeback" would be orthgonal feature. The goal is > > "let's save memory at the cost of *latency*". If the page is swapped-in > > soon, it's unfortunate. However, the design expects once it's swapped out, > > it means it's non-workingset so soonish swappined-in would be rather not > > many, theoritically compared to other workingset. > > If's it's too frequent, it means system were heavily overcommitted. > > Havid said, I agree it's not a good idea to enable incompressible page > writeback with idle page writeback. If you don't oppose, I want to add > new knob to "enable incompressible page writeback" so by default, > although we enable CONFIG_ZRAM_WRITEBACK, incompressible page writeback > is off until we enable the knob. > It would make some regressison if someone have used the feature but > I guess we are not too late. > > What do you think? Yes, totally works for me! "IDLE writeback" is superior to "incompressible writeback". "incompressible writeback" is completely unpredictable and uncontrollable; it depens on data patterns and compression algorithms. While "IDLE writeback" is predictable. I even suspect, that, *ideally*, we can remove "incompressible writeback". "IDLE pages" is a super set which also includes "incompressible" pages. So, technically, we still can do "incompressible writeback" from "IDLE writeback" path; but a much more reasonable one, based on a page idling period. I understand that you want to keep "direct incompressible writeback" around. ZRAM is especially popular on devices which do suffer from flash wearout, so I can see "incompressible writeback" path becoming a dead code, long term. -ss