linux-kernel - Re: Re: [PATCH] ARM: fix bug which VMALLOC

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Message-ID: <1441269272.3102.3.camel@pengutronix.de>
Date:	Thu, 03 Sep 2015 10:34:32 +0200
From:	Lucas Stach <l.stach@...gutronix.de>
To:	Yongtaek Lee <ytk.lee@...sung.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: Re: [PATCH] ARM: fix bug which VMALLOC_START is lowwer than
 0xf0000000

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@...sung.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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