linux-kernel - Re: [PATCH] mm: optionally disable brk()

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Message-ID: <888e62e0-3979-207b-c516-ddfc6b9f3345@redhat.com>
Date:   Mon, 5 Oct 2020 11:13:48 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>, Topi Miettinen <toiwoton@...il.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: optionally disable brk()

On 05.10.20 08:12, Michal Hocko wrote:
> On Sat 03-10-20 00:44:09, Topi Miettinen wrote:
>> 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.
> 
> I do not think we want to have config per syscall, do we? 

I do wonder if grouping would be a better option then (finding a proper
level of abstraction ...).

-- 
Thanks,

David / dhildenb