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 79D8CE77180 for ; Thu, 12 Dec 2024 08:50:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0C0276B0092; Thu, 12 Dec 2024 03:50:38 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 070C76B0093; Thu, 12 Dec 2024 03:50:38 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E7AC16B0095; Thu, 12 Dec 2024 03:50:37 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id C2E1C6B0092 for ; Thu, 12 Dec 2024 03:50:37 -0500 (EST) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 7032FC19D2 for ; Thu, 12 Dec 2024 08:50:37 +0000 (UTC) X-FDA: 82885685652.04.01816E6 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf22.hostedemail.com (Postfix) with ESMTP id 7500AC0003 for ; Thu, 12 Dec 2024 08:50:09 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=BHKg5MGs; spf=none (imf22.hostedemail.com: domain of BATV+197d639d84551e46db20+7781+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+197d639d84551e46db20+7781+infradead.org+hch@bombadil.srs.infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1733993412; a=rsa-sha256; cv=none; b=14ts6h+pNfcqgWH7fAyGAYwuT5jyBYjV8dAoB/4N7ClrfhXTn8UvAS7OtOuFidklTvvMdR e4q1g8qtg5rIaHVhrt9cD0TH1qBW+ZtXrm+jDYwZ8Q4mXCvRnO9t8++Bv1ga/jghsxi3ok jRoLcCUgtTpMDRxKMj9IyglMaRuYqto= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=BHKg5MGs; spf=none (imf22.hostedemail.com: domain of BATV+197d639d84551e46db20+7781+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+197d639d84551e46db20+7781+infradead.org+hch@bombadil.srs.infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1733993412; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ADWqa+CgY83FfhMvVQkSxseNW/G/vbE3oWskKPFMxG8=; b=EaFwlaWZbJZiHt6H5zp9r5el3NVv1HutfhhHQrdK4SYEcHe+uq9iMteVLmS9h6A0pl1RbV lKOmh8nA7dP5cqRwbtoTGJ/Vf7yKN3d1V58wDP+sNgcGGqOqL5WZpGhBh8Fcp71/pev/Ew vtNHMOZhoaYumtFPYjizx8LZrGx6E98= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=ADWqa+CgY83FfhMvVQkSxseNW/G/vbE3oWskKPFMxG8=; b=BHKg5MGs3ZTcFJI27mpOtM4XOa 9ZCPr9Eb3qofDwIUblO4ukocutHWKGiMoRQMLtBbHXxnCoXMDrZHdUQHYhYMFweo8RGxvACcHkZI9 di7WbfCETuyUZHH0O2/wWd6HpaCEvSsVISoEIYljyJEVjS4k4svrsTcYmlsoMZ83OC8/nAXmqmQyv u7PcCaRMkgMRezaJK67CQXLehry6o7gtGEZZfGH/L5t4t9OLafK1KlrhbGhW8WFkhl3NleLBPx798 hm4MRv4DrEqvO/SFfmHC6NRvnf8NyWEHkHdOgBSrBnNP3/OmQTuFdphYnH5sRV6QMANL0puq/gGZS dYV7xp0A==; Received: from hch by bombadil.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tLety-0000000HNHF-2dts; Thu, 12 Dec 2024 08:50:30 +0000 Date: Thu, 12 Dec 2024 00:50:30 -0800 From: Christoph Hellwig To: Barry Song <21cnbao@gmail.com> Cc: Christoph Hellwig , akpm@linux-foundation.org, linux-mm@kvack.org, axboe@kernel.dk, bala.seshasayee@linux.intel.com, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, kanchana.p.sridhar@intel.com, kasong@tencent.com, nphamcs@gmail.com, ryan.roberts@arm.com, senozhatsky@chromium.org, terrelln@fb.com, usamaarif642@gmail.com, v-songbaohua@oppo.com, wajdi.k.feghali@intel.com, willy@infradead.org, ying.huang@linux.alibaba.com, yosryahmed@google.com, baolin.wang@linux.alibaba.com Subject: Re: [PATCH RFC] mm: map zero-filled pages to zero_pfn while doing swap-in Message-ID: References: <20241212073711.82300-1-21cnbao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: 7500AC0003 X-Stat-Signature: ec4k78cq83w5qunzk6nupdb7p7jea1kt X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1733993409-882277 X-HE-Meta: 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 2fEOgws6 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 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: List-Subscribe: List-Unsubscribe: On Thu, Dec 12, 2024 at 09:46:03PM +1300, Barry Song wrote: > On Thu, Dec 12, 2024 at 9:29 PM Christoph Hellwig wrote: > > > > On Thu, Dec 12, 2024 at 08:37:11PM +1300, Barry Song wrote: > > > From: Barry Song > > > > > > While developing the zeromap series, Usama observed that certain > > > workloads may contain over 10% zero-filled pages. This may present > > > an opportunity to save memory by mapping zero-filled pages to zero_pfn > > > in do_swap_page(). If a write occurs later, do_wp_page() can > > > allocate a new page using the Copy-on-Write mechanism. > > > > Shouldn't this be done during, or rather instead of swap out instead? > > Swapping all zero pages out just to optimize the in-memory > > representation on seems rather backwards. > > I’m having trouble understanding your point—it seems like you might > not have fully read the code. :-) I've not read the code at all, I've read your commit log. > The situation is as follows: for a zero-filled page, we are currently > allocating a new > page unconditionally. By mapping this zero-filled page to zero_pfn, we could > save the memory used by this page. Yes. But why do that in swap-in and not swap-out?