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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 404A4CDB46E for ; Thu, 12 Oct 2023 15:02:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376440AbjJLPCt (ORCPT ); Thu, 12 Oct 2023 11:02:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346817AbjJLPCp (ORCPT ); Thu, 12 Oct 2023 11:02:45 -0400 Received: from out-194.mta0.migadu.com (out-194.mta0.migadu.com [IPv6:2001:41d0:1004:224b::c2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 06865E1 for ; Thu, 12 Oct 2023 08:02:40 -0700 (PDT) Date: Fri, 13 Oct 2023 00:02:26 +0900 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1697122956; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=RjcViyd2Fhk9iMtsIB4L9gySKen/F6NsFGsZ37IiSaI=; b=qh+sQi2+AwZtf3yb3TP3gZd3g09JYVCgAhKSM0xfGCLiCjjbUT1m8mW0IXi82EI3en1N5y 662DXTq/zsHoGArFquLa7xUi8nhZWazc5X+jWaJzY330XkHMienfF6P23UKc3/lVGIgLgc LoYahsX5YZ2pV4nsunvhAg/CM0Ks1AY= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Naoya Horiguchi To: David Hildenbrand Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , "Kirill A. Shutemov" , Mike Kravetz , Miaohe Lin , Vlastimil Babka , Muchun Song , Naoya Horiguchi , linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 0/5] mm, kpageflags: support folio and fix output for compound pages Message-ID: <20231012150226.GA473412@u2004> References: <20231010142801.3780917-1-naoya.horiguchi@linux.dev> <63d119f7-5adb-861a-00c2-69a92b19ef9b@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <63d119f7-5adb-861a-00c2-69a92b19ef9b@redhat.com> X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 12, 2023 at 10:33:04AM +0200, David Hildenbrand wrote: > On 10.10.23 16:27, Naoya Horiguchi wrote: > > Hi everyone, > > > > This patchset addresses 2 issues in /proc/kpageflags. > > > > 1. We can't easily tell folio from thp, because currently both pages are > > judged as thp, and > > 2. we see some garbage data in records of compound tail pages because > > we use tail pages to store some internal data. > > > > These issues require userspace programs to do additional work to understand > > the page status, which makes situation more complicated. > > > > This patchset tries to solve these by defining KPF_FOLIO for issue 1., and > > by hiding part of page flag info on tail pages of compound pages for issue 2. > > > > I think that technically some compound pages like thp/hugetlb/slab could be > > considered as folio, but in this version KPF_FOLIO is set only on folios > > At least thp+hugetlb are most certainly folios. Regarding slab, I suspect we > no longer call them folios (cannot be mapped to user space). But Im not sure > about the type hierarchy. I'm not sure about the exact definition of "folio", and I think it's better to make KPF_FOLIO set based on the definition. "being mapped to userspace" can be one possible criteria for the definition. But reading source code, folio_slab() and slab_folio() convert between struct slab and struct folio, so I feel that someone might think a slab is a kind of folio. > > > in pagecache (so "folios in narrower meaning"). I'm not confident about > > this choice, so if you have any idea about this, please let me know. > > It does sound inconsistent. What exactly do you want to tell user space with > the new flag? The current most problematic behavior is to report folio as thp (order-2 pagecache page is definitely a folio but not a thp), and this is what the new flag is intended to tell. Thanks, Naoya Horiguchi