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[88.114.211.119]) by smtp.gmail.com with ESMTPSA id m1sm667520lfr.32.2020.10.02.14.44.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 Oct 2020 14:44:11 -0700 (PDT) Subject: Re: [PATCH] mm: optionally disable brk() To: David Hildenbrand , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20201002171921.3053-1-toiwoton@gmail.com> <653873ef-2a57-37e0-1ac3-fba763652b35@redhat.com> From: Topi Miettinen Message-ID: <2a0f5ade-d770-c36e-50bc-ff0c8e9dacbf@gmail.com> Date: Sat, 3 Oct 2020 00:44:09 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <653873ef-2a57-37e0-1ac3-fba763652b35@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2.10.2020 20.52, David Hildenbrand wrote: > On 02.10.20 19:19, Topi Miettinen wrote: >> The brk() system call allows to change data segment size (heap). This >> is mainly used by glibc for memory allocation, but it can use mmap() >> and that results in more randomized memory mappings since the heap is >> always located at fixed offset to program while mmap()ed memory is >> randomized. > > Want to take more Unix out of Linux? > > Honestly, why care about disabling? User space can happily use mmap() if > it prefers. brk() interface doesn't seem to be used much and glibc is happy to switch to mmap() if brk() fails, so why not allow disabling it optionally? If you don't care to disable, don't do it and this is even the default. -Topi