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 2D2B7C76196 for ; Fri, 7 Apr 2023 10:15:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A431D900003; Fri, 7 Apr 2023 06:15:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9CCDD900002; Fri, 7 Apr 2023 06:15:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 89417900003; Fri, 7 Apr 2023 06:15:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 79BCF900002 for ; Fri, 7 Apr 2023 06:15:02 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 36B741C6E26 for ; Fri, 7 Apr 2023 10:15:02 +0000 (UTC) X-FDA: 80654186844.04.B5C9005 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf15.hostedemail.com (Postfix) with ESMTP id 3074AA0002 for ; Fri, 7 Apr 2023 10:14:59 +0000 (UTC) Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=cXZpGyfb; spf=pass (imf15.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=quarantine) header.from=collabora.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1680862500; 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=HEDYAre0fg9B8YDT55WIUxXXy5OFMG516N1Kug42LSQ=; b=7ddEeq9q3eaztaWCftKGenwqe3YjiOZcQm58NOOHrthRg/7nG2tLOBHM/M1Ms6EAQ/Eso3 7fsjbw+naYEX+pDslg3rST3lcGiU3sH2EHEverWjbx4nVm6uwnz1xaUW6tOsvKXpPS4/cL eyWJgCB7VRCqUyGG/AA3gWNLWMA+fro= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=cXZpGyfb; spf=pass (imf15.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com; dmarc=pass (policy=quarantine) header.from=collabora.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1680862500; a=rsa-sha256; cv=none; b=yNtTH64P4rO1i1jKPbGLoJ8uX9XJVGUXNsSwJxKlMYJOJuY17Ap1QVPcOtNV2T+9oun3yo Oh3WzmWCjVcelhs1tdwkQCT1+zridXAyvhzHXHXVmNHqFCethNTsQMwF42Vxc8sApCr1Rm 81wuOOKdQcBYP2GMsMnAZlGAlnuy92I= Received: from [192.168.10.39] (unknown [119.155.57.40]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madras.collabora.co.uk (Postfix) with ESMTPSA id 637A46603131; Fri, 7 Apr 2023 11:14:52 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1680862498; bh=9WP6pUpBkOjkcvFCjLQ/X0oqCxKf/YO1tbGg0IwaD8g=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=cXZpGyfbBDqWqi9rMvJzyzWzubRZSu9ZlI+W4zmtflNBkvxlViQd2BU5RAr7Rb2Xb zgsym/vALXf5K1nMX2MfNXL6VmHmmDgVMTocbmjp2LTDUH4Xz43C+q5YYfHLYHz7ho 9viO3eJkjQUYJvB8MB6IMDAWq0Xqn8UXep3s6yZTtXm1X9FbaJW0B5blLUvnpy6Zge aU5fIqi3eBVWRKrouL0yLn7dgictkTDyK0VYY1yyUVZaH52po+CYg5e0Mgs1M3PWmy wByDH8kZ/Qwiet4sxyGVYesTr62q6iKAr98uEPY6dzO4DUJJrmruewJ9traJ8MEioM X06VRpYxIA9LQ== Message-ID: Date: Fri, 7 Apr 2023 15:14:47 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Cc: Muhammad Usama Anjum , Peter Xu , David Hildenbrand , Andrew Morton , Andrei Vagin , Danylo Mocherniuk , Paul Gofman , Cyrill Gorcunov , Mike Rapoport , Nadav Amit , Alexander Viro , Shuah Khan , Christian Brauner , Yang Shi , Vlastimil Babka , "Liam R . Howlett" , Yun Zhou , Suren Baghdasaryan , Alex Sierra , Matthew Wilcox , Pasha Tatashin , Axel Rasmussen , "Gustavo A . R . Silva" , Dan Williams , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Greg KH , kernel@collabora.com Subject: Re: [PATCH v12 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs To: =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= References: <20230406074005.1784728-1-usama.anjum@collabora.com> <20230406074005.1784728-3-usama.anjum@collabora.com> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3074AA0002 X-Stat-Signature: ppqh9iz6h4ao487t5de9p3ty5zgzdroh X-HE-Tag: 1680862499-801018 X-HE-Meta: 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 ZMAb5QU0 sbCAm8yJLlrNpR/uGhGcYUfYSFgA+y4oV4TlTkRqXHxf58s2kkPgqeJAqPyplkLN2G0wbVnYWiEYrPz3k8wsIC0A5ejSYAmy+JqT9sRsbjpN6w+n8YGGFheD5HsZTt7QQNJ8z3GIfMTKJZv8Mh1/mfLCwIbnuiZYbateEYsn705FoWByRfTDnL9SP0ToQDJ9Gip0ya1sIt+T8DxkltI6QjrCS7fG5WKeSEJc0ZMFzugxFHo/bOvh9D78kAkV21YI3knF2QYw1VBgFAQmI7pN2MR3GrjRo6D5w6XOc+VEq7ntFSEuOx1ZYLNEYUjE/dt4L3S5kwZEiKpPaVjuk5AsfAnSw5qn9DAnKrwZJS1aRZTF+/amz1DqXWdRM0E2MFS3XjYm4 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 4/7/23 3:04 PM, Michał Mirosław wrote: > On Fri, 7 Apr 2023 at 11:35, Muhammad Usama Anjum > wrote: >> On 4/7/23 12:23 PM, Michał Mirosław wrote: >>> On Thu, 6 Apr 2023 at 23:12, Muhammad Usama Anjum >>> wrote: >>>> On 4/7/23 1:12 AM, Michał Mirosław wrote: >>>>> On Thu, 6 Apr 2023 at 09:40, Muhammad Usama Anjum >>>>> wrote: >>>>> [...] >>>>>> --- a/fs/proc/task_mmu.c >>>>>> +++ b/fs/proc/task_mmu.c >>>>> [...] >>>>>> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, >>>>>> + unsigned long end, struct mm_walk *walk) >>>>>> +{ >>> [...] >>>>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>>>>> + ptl = pmd_trans_huge_lock(pmd, vma); >>>>>> + if (ptl) { >>>>> [...] >>>>>> + return ret; >>>>>> + } >>>>>> +process_smaller_pages: >>>>>> + if (pmd_trans_unstable(pmd)) >>>>>> + return 0; >>>>> >>>>> Why pmd_trans_unstable() is needed here and not only after split_huge_pmd()? >>>> I'm not entirely sure. But the idea is if THP is unstable, we should >>>> return. As it doesn't seem like after splitting THP can be unstable, we >>>> should not check it. Do you agree with the following? >>> >>> The description of pmd_trans_unstable() [1] seems to indicate that it >>> is needed only after split_huge_pmd(). >>> >>> [1] https://elixir.bootlin.com/linux/v6.3-rc5/source/include/linux/pgtable.h#L1394 >> Sorry, yeah pmd_trans_unstable() is need after split. But it is also needed >> in normal case when ptl is NULL to rule out the case if pmd is unstable >> before performing operation on normal pages: >> >> ptl = pmd_trans_huge_lock(pmd, vma); >> if (ptl) { >> ... >> } >> if (pmd_trans_unstable(pmd)) >> return 0; >> >> This file has usage examples of pmd_trans_unstable(): >> >> https://elixir.bootlin.com/linux/v6.3-rc5/source/fs/proc/task_mmu.c#L634 >> https://elixir.bootlin.com/linux/v6.3-rc5/source/fs/proc/task_mmu.c#L1195 >> https://elixir.bootlin.com/linux/v6.3-rc5/source/fs/proc/task_mmu.c#L1543 >> https://elixir.bootlin.com/linux/v6.3-rc5/source/fs/proc/task_mmu.c#L1887 >> >> So we are good with what we have in this patch. > > Shouldn't we signal ACTION_AGAIN then in order to call .pte_hole? I'm not sure. I've not done research on it if we need to signal ACTION_AGAIN as this function pagemap_scan_pmd_entry() mimics how pagemap_pmd_range() handles reads to the pagemap file. pagemap_pmd_range() isn't doing anything if pmd is unstable. Hence we also not doing anything. > > Best Regards > Michał Mirosław -- BR, Muhammad Usama Anjum