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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 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 Subject: Re: [PATCH v3 0/4] Implement IOCTL to get and clear soft dirty PTE Content-Language: en-US From: Muhammad Usama Anjum To: Danylo Mocherniuk , avagin@gmail.com, linux-mm@kvack.org, akpm@linux-foundation.org, gregkh@linuxfoundation.org References: <20221014134802.1361436-1-mdanylo@google.com> <474513c0-4ff9-7978-9d77-839fe775d04c@collabora.com> In-Reply-To: <474513c0-4ff9-7978-9d77-839fe775d04c@collabora.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; 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dkim=pass header.d=collabora.com header.s=mail header.b=AU6QgCCT; spf=pass (imf21.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=none) header.from=collabora.com X-Stat-Signature: oj6byb9hkbz6kcn9m6h5b8jyqmh9jcos X-Rspamd-Queue-Id: D8FEE1C002A X-HE-Tag: 1666099976-710188 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 10/18/22 3:36 PM, Muhammad Usama Anjum wrote: >>>>>>> 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. > Updated interface with only one IOCTL. If vec is defined, get operation will be performed. If PAGEMAP_SD_CLEAR flag is specified, soft dirty bit will be cleared as well. CLEAR flag can only be specified for clearing soft dirty bit. /* PAGEMAP IOCTL */ #define PAGEMAP_SCAN _IOWR('f', 16, 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 of the page * @len: Length of the region (All the pages in this length are included) * @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: Required mask - All of these bits have to be set * @amask: Any mask - Any of these bits are set * @emask: Exclude mask - None of these bits are set * @rmask: Bits that have to be reported to the user in page_region */ struct pagemap_scan_args { __u64 __user start; __u64 len; __u64 __user vec; __u64 vec_len; __u32 max_out_page; __u32 flags; __u32 rmask; __u32 amask; __u32 emask; __u32 rmask; }; /* Special flags */ #define PAGEMAP_SD_CLEAR 1 << 0 #define PAGEMAP_NO_REUSED_REGIONS 1 << 1 > /* 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 >>