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 BB2C5C433FE for ; Tue, 18 Oct 2022 10:36:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D5E676B0072; Tue, 18 Oct 2022 06:36:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D0EF56B0075; Tue, 18 Oct 2022 06:36:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BFD3F6B0078; Tue, 18 Oct 2022 06:36:38 -0400 (EDT) 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 B06726B0072 for ; Tue, 18 Oct 2022 06:36:38 -0400 (EDT) Received: from smtpin04.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 69B51120F2B for ; Tue, 18 Oct 2022 10:36:38 +0000 (UTC) X-FDA: 80033716476.04.515AF72 Received: from madras.collabora.co.uk (madras.collabora.co.uk [46.235.227.172]) by imf30.hostedemail.com (Postfix) with ESMTP id BEA8580030 for ; Tue, 18 Oct 2022 10:36:37 +0000 (UTC) Received: from [192.168.10.9] (unknown [39.45.244.84]) (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 D95546602362; Tue, 18 Oct 2022 11:36:29 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1666089396; bh=6IXmqpcqcRFcfMJiig2n7Q1DNwmUnPwfuYR6Uqnx6Yc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=D03y7t3QjoZFHOlkcoh8Upt8tFLOo1WMcBG3pRMvPqs8KSRbs/30kAv6zWdk6/Vet yippPqeMjF7picY35GU2KggxzY89zHYPmFTAqYQOzbhhX85wzpEBhXqzP1SVVNDkFL odcgunCsKvKq7zvsizOgNNEDDDrT14oXuW2m4DFtUBtk4r40pppLo6J9IICdvw+egA MPLWSElufJKkoaSv44NnTEa3VpeSJNuw0h5fEidG1XpWBlKsUT6m/sL0ChrH+fMlu9 TMaNQweRWpJp1eIdqcpk18x1bGqZnqfaKL8leKd5csF9hIvavkqoFCwX94yB//YktH h4W10JmoUxXOQ== Message-ID: <474513c0-4ff9-7978-9d77-839fe775d04c@collabora.com> Date: Tue, 18 Oct 2022 15:36:24 +0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: [PATCH v3 0/4] Implement IOCTL to get and clear soft dirty PTE Content-Language: en-US To: Danylo Mocherniuk , avagin@gmail.com, linux-mm@kvack.org, akpm@linux-foundation.org, gregkh@linuxfoundation.org Cc: corbet@lwn.net, david@redhat.com, kernel@collabora.com, krisman@collabora.com, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, peter.enderborg@sony.com, shuah@kernel.org, viro@zeniv.linux.org.uk, willy@infradead.org, emmir@google.com, figiel@google.com, kyurtsever@google.com, Paul Gofman , surenb@google.com References: <20221014134802.1361436-1-mdanylo@google.com> From: Muhammad Usama Anjum In-Reply-To: <20221014134802.1361436-1-mdanylo@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666089398; 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=AmYX8ODo3DeG8b4jYtaMieoGFqyy5l5lIciYZuLqE9g=; b=i+0yyVYyTQSiFOefBpovJI6I0yp+pGw74ovGPgrnejOKl/DLl0sYxlu+hGtUiJWJmcW8xe HqZzP8cdEFHfmCmSNmT4DPeweepkCKO4ivxCzwJyGgybCRXjudEjbmnApSIq1J+xi7RMmQ oXfw1uI4JxBk22tjU6BKNWiiYO8lrQk= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=D03y7t3Q; dmarc=pass (policy=none) header.from=collabora.com; spf=pass (imf30.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666089398; a=rsa-sha256; cv=none; b=TnwUQljCNvoGsksbZkyQVmluRWzSP+PjVc33uog5U6ZVe5n13cYHlBpf1A/BzCu8OvYnNv robYkRfwfTMXjwztjDJVdZvBRoFaYIfu3rTv1BlRaV97KvaTS8bnKiqVaHle8LBHE14M+O Zk6z/ncW8dU9NxiK6O5s0H80lNKYe9U= Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=collabora.com header.s=mail header.b=D03y7t3Q; dmarc=pass (policy=none) header.from=collabora.com; spf=pass (imf30.hostedemail.com: domain of usama.anjum@collabora.com designates 46.235.227.172 as permitted sender) smtp.mailfrom=usama.anjum@collabora.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BEA8580030 X-Rspam-User: X-Stat-Signature: k48wrf5yzckma8wgusa3j3acr3a3ijaz X-HE-Tag: 1666089397-165032 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: >>>>>> I mean we should be able to specify for what pages we need to get info >>>>>> for. An ioctl argument can have these four fields: >>>>>> * required bits (rmask & mask == mask) - all bits from this mask have to be set. >>>>>> * any of these bits (amask & mask != 0) - any of these bits is set. >>>>>> * exclude masks (emask & mask == 0) = none of these bits are set. >>>>>> * return mask - bits that have to be reported to user. >>> The required mask (rmask) makes sense to me. At the moment, I only know >>> about the practical use case for the required mask. Can you share how >>> can any and exclude masks help for the CRIU? >>> >> >> I looked at should_dump_page in the CRIU code: >> https://github.com/checkpoint-restore/criu/blob/45641ab26d7bb78706a6215fdef8f9133abf8d10/criu/mem.c#L102 >> >> When CRIU dumps file private mappings, it needs to get pages that have >> PME_PRESENT or PME_SWAP but don't have PME_FILE. > > I would really like to see the mask discussed will be adopted. With it CRIU will > be able to migrate huge sparse VMAs assuming that a single hole is processed in > O(1) time. > > Use cases for migrating sparse VMAs are binaries sanitized with ASAN, MSAN or > TSAN [1]. All of these sanitizers produce sparse mappings of shadow memory [2]. > Being able to migrate such binaries allows to highly reduce the amount of work > needed to identify and fix post-migration crashes, which happen constantly. > Hello all, I've included the masks which the CRIU developers have specified. max_out_page is another new optional variable which is needed to terminate the operation without visiting all the pages after finding the max_out_page number of desired pages. There is no way to terminate the operation without this variable. How does the interface looks now? Please comment. /* PAGEMAP IOCTL */ #define PAGEMAP_GET _IOWR('f', 16, struct pagemap_sd_args) #define PAGEMAP_CLEAR _IOWR('f', 17, struct pagemap_sd_args) #define PAGEMAP_GET_AND_CLEAR _IOWR('f', 18, struct pagemap_sd_args) /* Bits are set in the bitmap of the page_region and masks in pagemap_sd_args */ #define PAGE_IS_SD 1 << 0 #define PAGE_IS_FILE 1 << 1 #define PAGE_IS_PRESENT 1 << 2 #define PAGE_IS_SWAPED 1 << 3 /** * struct page_region - Page region with bitmap flags * @start: Start of the region * @len: Length of the region * bitmap: Bits sets for the region */ struct page_region { __u64 start; __u64 len; __u64 bitmap; }; /** * struct pagemap_sd_args - Soft-dirty IOCTL argument * @start: Starting address * @len: Length of the region * @vec: Output page_region struct array * @vec_len: Length of the page_region struct array * @max_out_page: Optional max output pages (It must be less than vec_len if specified) * @flags: Special flags for the IOCTL * @rmask: Special flags for the IOCTL * @amask: Special flags for the IOCTL * @emask: Special flags for the IOCTL * @__reserved: Reserved member to preserve data alignment. Must be 0. */ struct pagemap_sd_args { __u64 __user start; __u64 len; __u64 __user vec; // page_region __u64 vec_len; // sizeof(page_region) __u32 flags; // special flags __u32 rmask; __u32 amask; __u32 emask; __u32 max_out_page; __u32 __reserved; }; /* Special flags */ #define PAGEMAP_NO_REUSED_REGIONS 0x1 >> >>>>>>> - Clear the pages which are soft-dirty. >>>>>>> - The optional flag to ignore the VM_SOFTDIRTY and only track per page >>>>>>> soft-dirty PTE bit >>>>>>> >>>>>>> There are two decisions which have been taken about how to get the output >>>>>>> from the syscall. >>>>>>> - Return offsets of the pages from the start in the vec >>>>>> >>>>>> We can conside to return regions that contains pages with the same set >>>>>> of bits. >>>>>> >>>>>> struct page_region { >>>>>>       void *start; >>>>>>       long size; >>>>>>       u64 bitmap; >>>>>> } >>>>>> >>>>>> And ioctl returns arrays of page_region-s. I believe it will be more >>>>>> compact form for many cases. >>>>> Thank you for mentioning this. I'd considered this while development. >>>>> But I gave up and used the simple array to return the offsets of the >>>>> pages as in the problem I'm trying to solve, the dirty pages may be >>>>> present amid non-dirty pages. The range may not be useful in that case. >>>> >>>> This is a good example. If we expect more than two consequent pages >>>> on average, the "region" interface looks more prefered. I don't know your >>>> use-case, but in the case of CRIU, this assumption looks reasonable. > > Plus one for page_region data structure. It will make ASAN shadow memory > representation much more compact as well as any other classical use-case. > > [1] https://github.com/google/sanitizers > [2] https://github.com/google/sanitizers/wiki/AddressSanitizerAlgorithm#64-bit > > Best, > Danylo >