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Subject: Re: [PATCH RESEND 6/8] parisc: Use mmap_base, not mmap_legacy_base,
 as low_limit for bottom-up mmap
To:     Alexandre Ghiti <alex@ghiti.fr>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     "James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        "David S . Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
        sparclinux@vger.kernel.org, linux-mm@kvack.org
References: <20190620050328.8942-1-alex@ghiti.fr>
 <20190620050328.8942-7-alex@ghiti.fr>
From:   Helge Deller <deller@gmx.de>
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Date:   Tue, 25 Jun 2019 16:09:06 +0200
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On 20.06.19 07:03, Alexandre Ghiti wrote:
> Bottom-up mmap scheme is used twice:
>
> - for legacy mode, in which mmap_legacy_base and mmap_base are equal.
>
> - in case of mmap failure in top-down mode, where there is no need to go
> through the whole address space again for the bottom-up fallback: the go=
al
> of this fallback is to find, as a last resort, space between the top-dow=
n
> mmap base and the stack, which is the only place not covered by the
> top-down mmap.
>
> Then this commit removes the usage of mmap_legacy_base field from parisc
> code.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>

Boot-tested on parisc and seems to work nicely, thus:

Acked-by: Helge Deller <deller@gmx.de>

Helge


> ---
>  arch/parisc/kernel/sys_parisc.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_pa=
risc.c
> index 5d458a44b09c..e987f3a8eb0b 100644
> --- a/arch/parisc/kernel/sys_parisc.c
> +++ b/arch/parisc/kernel/sys_parisc.c
> @@ -119,7 +119,7 @@ unsigned long arch_get_unmapped_area(struct file *fi=
lp, unsigned long addr,
>
>  	info.flags =3D 0;
>  	info.length =3D len;
> -	info.low_limit =3D mm->mmap_legacy_base;
> +	info.low_limit =3D mm->mmap_base;
>  	info.high_limit =3D mmap_upper_limit(NULL);
>  	info.align_mask =3D last_mmap ? (PAGE_MASK & (SHM_COLOUR - 1)) : 0;
>  	info.align_offset =3D shared_align_offset(last_mmap, pgoff);
> @@ -240,13 +240,11 @@ static unsigned long mmap_legacy_base(void)
>   */
>  void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_st=
ack)
>  {
> -	mm->mmap_legacy_base =3D mmap_legacy_base();
> -	mm->mmap_base =3D mmap_upper_limit(rlim_stack);
> -
>  	if (mmap_is_legacy()) {
> -		mm->mmap_base =3D mm->mmap_legacy_base;
> +		mm->mmap_base =3D mmap_legacy_base();
>  		mm->get_unmapped_area =3D arch_get_unmapped_area;
>  	} else {
> +		mm->mmap_base =3D mmap_upper_limit(rlim_stack);
>  		mm->get_unmapped_area =3D arch_get_unmapped_area_topdown;
>  	}
>  }
>