linux-kernel - Re: [PATCH v5 14/14] riscv: Make mmap allocation top-down by default

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Date:   Wed, 31 Jul 2019 15:40:35 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Alexandre Ghiti <alex@...ti.fr>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Luis Chamberlain <mcgrof@...nel.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>, linux-fsdevel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-mips@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        linux-arm-kernel@...ts.infradead.org,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v5 14/14] riscv: Make mmap allocation top-down by
 default

On Tue, 30 Jul 2019, Alexandre Ghiti wrote:

> In order to avoid wasting user address space by using bottom-up mmap
> allocation scheme, prefer top-down scheme when possible.
> 
> Before:
> root@...uriscv64:~# cat /proc/self/maps
> 00010000-00016000 r-xp 00000000 fe:00 6389       /bin/cat.coreutils
> 00016000-00017000 r--p 00005000 fe:00 6389       /bin/cat.coreutils
> 00017000-00018000 rw-p 00006000 fe:00 6389       /bin/cat.coreutils
> 00018000-00039000 rw-p 00000000 00:00 0          [heap]
> 1555556000-155556d000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
> 155556d000-155556e000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
> 155556e000-155556f000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
> 155556f000-1555570000 rw-p 00000000 00:00 0
> 1555570000-1555572000 r-xp 00000000 00:00 0      [vdso]
> 1555574000-1555576000 rw-p 00000000 00:00 0
> 1555576000-1555674000 r-xp 00000000 fe:00 7187   /lib/libc-2.28.so
> 1555674000-1555678000 r--p 000fd000 fe:00 7187   /lib/libc-2.28.so
> 1555678000-155567a000 rw-p 00101000 fe:00 7187   /lib/libc-2.28.so
> 155567a000-15556a0000 rw-p 00000000 00:00 0
> 3fffb90000-3fffbb1000 rw-p 00000000 00:00 0      [stack]
> 
> After:
> root@...uriscv64:~# cat /proc/self/maps
> 00010000-00016000 r-xp 00000000 fe:00 6389       /bin/cat.coreutils
> 00016000-00017000 r--p 00005000 fe:00 6389       /bin/cat.coreutils
> 00017000-00018000 rw-p 00006000 fe:00 6389       /bin/cat.coreutils
> 2de81000-2dea2000 rw-p 00000000 00:00 0          [heap]
> 3ff7eb6000-3ff7ed8000 rw-p 00000000 00:00 0
> 3ff7ed8000-3ff7fd6000 r-xp 00000000 fe:00 7187   /lib/libc-2.28.so
> 3ff7fd6000-3ff7fda000 r--p 000fd000 fe:00 7187   /lib/libc-2.28.so
> 3ff7fda000-3ff7fdc000 rw-p 00101000 fe:00 7187   /lib/libc-2.28.so
> 3ff7fdc000-3ff7fe2000 rw-p 00000000 00:00 0
> 3ff7fe4000-3ff7fe6000 r-xp 00000000 00:00 0      [vdso]
> 3ff7fe6000-3ff7ffd000 r-xp 00000000 fe:00 7193   /lib/ld-2.28.so
> 3ff7ffd000-3ff7ffe000 r--p 00016000 fe:00 7193   /lib/ld-2.28.so
> 3ff7ffe000-3ff7fff000 rw-p 00017000 fe:00 7193   /lib/ld-2.28.so
> 3ff7fff000-3ff8000000 rw-p 00000000 00:00 0
> 3fff888000-3fff8a9000 rw-p 00000000 00:00 0      [stack]
> 
> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>

Acked-by: Paul Walmsley <paul.walmsley@...ive.com> # for arch/riscv

As Alex notes, this patch depends on "[PATCH] riscv: kbuild: add virtual 
memory system selection":

https://lore.kernel.org/linux-riscv/alpine.DEB.2.21.9999.1907301218560.3486@viisi.sifive.com/T/#t

which will likely go up during v5.3-rc.


- Paul