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 B2103EB64DD for ; Mon, 7 Aug 2023 04:28:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229976AbjHGE2l (ORCPT ); Mon, 7 Aug 2023 00:28:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35374 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229719AbjHGE2d (ORCPT ); Mon, 7 Aug 2023 00:28:33 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D34F410F6; Sun, 6 Aug 2023 21:28:31 -0700 (PDT) Received: from [192.168.100.7] (unknown [39.34.184.20]) (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 4BA076607095; Mon, 7 Aug 2023 05:28:24 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1691382510; bh=wyfC01K6b0rH0xfssr+2AthD/ZY4mDdRepl4Mcer+1Y=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=iFs9XlTi8bs3WTdv05bVWWsLMcOgXgBfvOnKLeAilg75v6YB/L/h+l+ECUKsHZN91 s92AZhJygXX5nqG1ZeMv6N2Yz+kHunuKuML9taIZnomjB/odsIFKjRWQPvF62Vwxh0 MagPXlH8/VI4cR7v9T3R17x/sQ3YBAnAEHrl5qGaiD8l0/j6dMR4LnLFAlKdzep6t5 H71sS2QLyLIO1OAIV4ac9DIgCAtfeg2N+0u3L2V7nlPvaKhU+aehUuzd6cJNtNvPqq NXtNBan9kc+1m5j/u5KUYWVIgyFhuW7J/B4sn6Trcsy0k4ci9lOyWgojHJCGq6Kkm0 D9qvM2Q3bKtbw== Message-ID: <10f947a2-3917-a5fe-837d-214d70991bcb@collabora.com> Date: Mon, 7 Aug 2023 09:28:19 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.1 Cc: Muhammad Usama Anjum , Peter Xu , David Hildenbrand , Andrew Morton , =?UTF-8?B?TWljaGHFgiBNaXJvc8WC?= =?UTF-8?Q?aw?= , 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, =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= Subject: Re: [PATCH v26 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs To: Andrei Vagin References: <20230727093637.1262110-1-usama.anjum@collabora.com> <20230727093637.1262110-3-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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/5/23 2:53 AM, Andrei Vagin wrote: > On Thu, Jul 27, 2023 at 2:37 AM Muhammad Usama Anjum > wrote: >> > > > >> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) >> +{ >> + unsigned long walk_start, walk_end; >> + struct mmu_notifier_range range; >> + struct pagemap_scan_private p; >> + size_t n_ranges_out = 0; >> + int ret; >> + >> + memset(&p, 0, sizeof(p)); >> + ret = pagemap_scan_get_args(&p.arg, uarg); >> + if (ret) >> + return ret; >> + >> + ret = pagemap_scan_init_bounce_buffer(&p); >> + if (ret) >> + return ret; >> + >> + /* Protection change for the range is going to happen. */ >> + if (p.arg.flags & PM_SCAN_WP_MATCHING) { >> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0, >> + mm, p.arg.start, p.arg.end); >> + mmu_notifier_invalidate_range_start(&range); >> + } >> + >> + walk_start = walk_end = p.arg.start; >> + for (; walk_end != p.arg.end; walk_start = walk_end) { >> + int n_out; >> + >> + walk_end = min_t(unsigned long, >> + (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK, >> + p.arg.end); > > This approach has performance implications. The basic program that scans > its address space takes around 20-30 seconds, but it has just a few > small mappings. The first optimization that comes to mind is to remove > the PAGEMAP_WALK_SIZE limit and instead halt walk_page_range when the > bounce buffer is full. After draining the buffer, the walk_page_range > function can be restarted. Yeah, I've this implemented in WIP and will be posting in next revision. > > The test program and perf data can be found here: > https://gist.github.com/avagin/c5a22f3c78f8cb34281602dfe9c43d10 > >> + >> + ret = mmap_read_lock_killable(mm); >> + if (ret) >> + break; >> + ret = walk_page_range(mm, walk_start, walk_end, >> + &pagemap_scan_ops, &p); >> + mmap_read_unlock(mm); >> + >> + n_out = pagemap_scan_flush_buffer(&p); >> + if (n_out < 0) >> + ret = n_out; >> + else >> + n_ranges_out += n_out; >> + >> + if (ret) >> + break; >> + } >> + > > Thanks, > Andrei -- BR, Muhammad Usama Anjum