From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [PATCH] xen/arm: Workaround for memory problem >1gb
 on last section
Date: Thu, 02 Oct 2014 12:03:36 +0100
Message-ID: <542D3108.4080506@linaro.org>
References: <CAHt6W4cs7zX3qRsk4_AibXoC+jZ85E5+WXz_WAO6CA_-udkPEw@mail.gmail.com>
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To: Frediano Ziglio <freddy77@gmail.com>
Cc: Tim Deegan <tim@xen.org>, Stefano Stabellini <stefano.stabellini@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

Hello Frediano,

On 10/01/2014 03:27 PM, Frediano Ziglio wrote:
> setup_xenheap_mappings setup head memory on Arm 32 has a limit of 1gb.
> On system with large memory is possible that there are no blocks of memory
> smaller than 1gb leading xenheap_pages to be more than 1gb.
> This cause memory errors trying to access heap after the 1gb limit.
> 
> Signed-off-by: Frediano Ziglio <frediano.ziglio@huawei.com>
> ---
>  xen/arch/arm/setup.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 446de8a..b1a43e6 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -524,6 +524,9 @@ static void __init setup_mm(unsigned long
> dtb_paddr, size_t dtb_size)
>      if ( ! e )
>          panic("Not not enough space for xenheap");
> 
> +    if ( xenheap_pages > 1<<(30-PAGE_SHIFT) )
> +        xenheap_pages = 1<<(30-PAGE_SHIFT);
> +

Looking closer to the code, can't we add a new constraint before the
loop when we are looking for the maximum heap size?

smth like:

xenheap_pages = (heap_pages/8 + ...)
xenheap_pages = max(xenheap_pages, 128UL<<(20 - PAGE_SHIFT)
xenheap_pages = max(xenheap_pages, 1UL<<(30-PAGE_SHIFT))

Regards,

-- 
Julien Grall