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[85.71.35.39]) by smtp.gmail.com with ESMTPSA id p15sm27989090wrt.15.2021.02.01.11.19.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Feb 2021 11:19:24 -0800 (PST) Subject: Re: Very slow unlockall() To: Vlastimil Babka , Michal Hocko Cc: linux-mm@kvack.org, Linux Kernel Mailing List , Mikulas Patocka References: <70885d37-62b7-748b-29df-9e94f3291736@gmail.com> <20210108134140.GA9883@dhcp22.suse.cz> <9474cd07-676a-56ed-1942-5090e0b9a82f@suse.cz> <6eebb858-d517-b70d-9202-f4e84221ed89@suse.cz> From: Milan Broz Message-ID: Date: Mon, 1 Feb 2021 20:19:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <6eebb858-d517-b70d-9202-f4e84221ed89@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 01/02/2021 19:55, Vlastimil Babka wrote: > On 2/1/21 7:00 PM, Milan Broz wrote: >> On 01/02/2021 14:08, Vlastimil Babka wrote: >>> On 1/8/21 3:39 PM, Milan Broz wrote: >>>> On 08/01/2021 14:41, Michal Hocko wrote: >>>>> On Wed 06-01-21 16:20:15, Milan Broz wrote: >>>>>> Hi, >>>>>> >>>>>> we use mlockall(MCL_CURRENT | MCL_FUTURE) / munlockall() in cryptsetup code >>>>>> and someone tried to use it with hardened memory allocator library. >>>>>> >>>>>> Execution time was increased to extreme (minutes) and as we found, the problem >>>>>> is in munlockall(). >>>>>> >>>>>> Here is a plain reproducer for the core without any external code - it takes >>>>>> unlocking on Fedora rawhide kernel more than 30 seconds! >>>>>> I can reproduce it on 5.10 kernels and Linus' git. >>>>>> >>>>>> The reproducer below tries to mmap large amount memory with PROT_NONE (later never used). >>>>>> The real code of course does something more useful but the problem is the same. >>>>>> >>>>>> #include >>>>>> #include >>>>>> #include >>>>>> #include >>>>>> >>>>>> int main (int argc, char *argv[]) >>>>>> { >>>>>> void *p = mmap(NULL, 1UL << 41, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > So, this is 2TB memory area, but PROT_NONE means it's never actually populated, > although mlockall(MCL_CURRENT) should do that. Once you put PROT_READ | > PROT_WRITE there, the mlockall() starts taking ages. > > So does that reflect your use case? munlockall() with large PROT_NONE areas? If > so, munlock_vma_pages_range() is indeed not optimized for that, but I would > expect such scenario to be uncommon, so better clarify first. It is just a simple reproducer of the underlying problem, as suggested here https://gitlab.com/cryptsetup/cryptsetup/-/issues/617#note_478342301 We use mlockall() in cryptsetup and with hardened malloc it slows down unlock significantly. (For the real case problem please read the whole issue report above.) m.