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SubjectRe: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than 0xf0000000
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Am Donnerstag, den 03.09.2015, 17:28 +0900 schrieb Yongtaek Lee:
> > On Thu, Sep 03, 2015 at 11:24:47AM +0900, Yongtaek Lee wrote:
> > > default value of vmalloc_min was set 0xf0000000 for ARM by commit
> > > 0536bdf3. But actually vmalloc_min is 0xef800000 not 0xf0000000.
> > >
> > > VMALLOC_END - (240 << 20) - VMALLOC_OFFSET)
> > > 0xff000000 - 0x0f000000 - 0x00800000 = 0xef800000
> > >
> > > In case of 768MB ram without CONFIG_HIGHMEM=y, last 8MB could not be
> > > allocated. Kernel log also print out warning message as below.
> > > "Truncating RAM at 80000000-afffffff to -af7fffff (vmalloc region overlap)."
> > >
> > > Although it could be solved by state "vmalloc=size" in cmdline but i think
> > > it would be better to change default value to 232 from 240.
> > >
> > > Signed-off-by: Yongtaek Lee <ytk.lee@samsung.com>
> >
> > I fail to see what the problem is here. You're adjusting the size of the
> > vmalloc space to accomodate the size of RAM you have. That's not a bug.
>
> I will explain more about problem.
> It could happened with 768MB RAM device and CONFIG_HIGHMEN is not set.
> "vmalloc=size" also not stated so that default value of vmalloc_min will be
> used to calculate lowmem end address.

> before applying patch.
> [ 0.000000] [0: swapper: 0] [c0] Truncating RAM at 80000000-afffffff to -af7fffff (vmalloc region overlap).
>
> [ 0.000000] [0: swapper: 0] [c0] Memory: 106MB 652MB = 758MB total
> [ 0.000000] [0: swapper: 0] [c0] Memory: 669892k/669892k available, 108348k reserved, 0K highmem
> [ 0.000000] [0: swapper: 0] [c0] Virtual kernel memory layout:
> [ 0.000000] [0: swapper: 0] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
> [ 0.000000] [0: swapper: 0] fixmap : 0xfff00000 - 0xfffe0000 ( 896 kB)
> [ 0.000000] [0: swapper: 0] vmalloc : 0xf0000000 - 0xff000000 ( 240 MB)
> [ 0.000000] [0: swapper: 0] lowmem : 0xc0000000 - 0xef800000 ( 760 MB)
> [ 0.000000] [0: swapper: 0] modules : 0xbf000000 - 0xc0000000 ( 16 MB)
> [ 0.000000] [0: swapper: 0] .text : 0xc0008000 - 0xc09bbee0 (9936 kB)
> [ 0.000000] [0: swapper: 0] .init : 0xc09bc000 - 0xc0a2b740 ( 446 kB)
> [ 0.000000] [0: swapper: 0] .data : 0xc0a2c000 - 0xc0ac4088 ( 609 kB)
> [ 0.000000] [0: swapper: 0] .bss : 0xc0ac4088 - 0xc0d3e7b4 (2538 kB)
>
> after applying patch.
> [ 0.000000] [0: swapper: 0] [c0] Memory: 106MB 660MB = 766MB total
> [ 0.000000] [0: swapper: 0] [c0] Memory: 678004k/678004k available, 108428k reserved, 0K highmem
> [ 0.000000] [0: swapper: 0] [c0] Virtual kernel memory layout:
> [ 0.000000] [0: swapper: 0] vector : 0xffff0000 - 0xffff1000 ( 4 kB)
> [ 0.000000] [0: swapper: 0] fixmap : 0xfff00000 - 0xfffe0000 ( 896 kB)
> [ 0.000000] [0: swapper: 0] vmalloc : 0xf0800000 - 0xff000000 ( 232 MB)
> [ 0.000000] [0: swapper: 0] lowmem : 0xc0000000 - 0xf0000000 ( 768 MB)
> [ 0.000000] [0: swapper: 0] modules : 0xbf000000 - 0xc0000000 ( 16 MB)
> [ 0.000000] [0: swapper: 0] .text : 0xc0008000 - 0xc09bbee0 (9936 kB)
> [ 0.000000] [0: swapper: 0] .init : 0xc09bc000 - 0xc0a2b740 ( 446 kB)
> [ 0.000000] [0: swapper: 0] .data : 0xc0a2c000 - 0xc0ac4088 ( 609 kB)
> [ 0.000000] [0: swapper: 0] .bss : 0xc0ac4088 - 0xc0d3e7b4 (2538 kB)
>
> As i know "vmalloc=size" is not mandatory so that i think default value of
> vmalloc_min is wrong.
>
So, if we go and apply your logic to a 1GB system we should resize the
vmalloc area to 0 bytes in order to avoid RAM truncation without
CONFIG_HIGHMEM?

Sorry, but the only sane options here are to either live with the
truncation, enable CONFIG_HIGHMEM, or set vmalloc size manually.
Changing a default value that affects everyone for the benefit of your
specific use-case isn't a sane option.

Regards,
Lucas
--
Pengutronix e.K. | Lucas Stach |
Industrial Linux Solutions | http://www.pengutronix.de/ |



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