Re: [PATCH] x86: revert "x86: Fix S4 regression"

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Jul 25, 2012 at 09:19:08AM +0900, Takao Indoh wrote:
> (2012/07/25 0:55), Cong Wang wrote:
> >On Mon, 2012-07-23 at 20:22 +0900, Takao Indoh wrote:
> >>(2012/07/23 19:00), Dave Young wrote:
> >>>On 07/17/2012 11:15 AM, Takao Indoh wrote:
> >>>
> >>>>Hi Cong,
> >>>>
> >>>>When I tested kdump with 3.5.0-rc6 kernel, I found a problem of kdump
> >>>>kernel's panic in find_early_table_space().
> >>>>
> >>>>init_memory_mapping: [mem 0x00000000-0x36ffafff]
> >>>>Kernel panic - not syncing: Cannot find space for the kernel page tables
> >>>>Pid: 0, comm: swapper Not tainted 3.5.0-rc6 #17
> >>>>Call Trace:
> >>>>   [<ffffffff8158549b>] panic+0xb8/0x1c8
> >>>>   [<ffffffff8158565d>] ? printk+0x48/0x4a
> >>>>   [<ffffffff8157304c>] init_memory_mapping+0x46c/0x530
> >>>>   [<ffffffff818a73c7>] setup_arch+0x669/0xb0e
> >>>>   [<ffffffff8158565d>] ? printk+0x48/0x4a
> >>>>   [<ffffffff818a3a1f>] start_kernel+0x9b/0x34a
> >>>>   [<ffffffff818a332d>] x86_64_start_reservations+0x131/0x136
> >>>>   [<ffffffff818a341f>] x86_64_start_kernel+0xed/0xf4
> >>>>
> >>>>In find_early_table_space(), a kernel tries to find free area below 512M
> >>>>for pgtable using memblock_find_in_range, but it fails because kdump
> >>>>kernel does not have enough free space below 512M due to the memmap
> >>>>restriction. This is the memmap option specified against kdump kernel
> >>>>when crashkernel=128M.
> >>>>
> >>>>memmap=560K@64K memmap=130492K@770608K
> >>>>
> >>>>Only 560KB area is available and it is not sufficient for pgtable (it
> >>>>seems that about 1.8MB area is needed for pgtable). This problem is
> >>>>fixed by your revert patch. I hope this patch gets merged.
> >>>
> >>>
> >>>I can reproduce this issue as well, probably related to some x86 mm init
> >>>commits, this alloc failure does not happen with reverting below commits:
> >>>
> >>>bd2753b2dda7bb43c7468826de75f49c6a7e8965
> >>>722bc6b16771ed80871e1fd81c86d3627dda2ac8
> >>Yeah, my result of bisect is as follows and at first I thought the
> >>commit 722bc6 caused this regression.
> >>
> >>722bc6b16771ed80871e1fd81c86d3627dda2ac8 is the first bad commit
> >>commit 722bc6b16771ed80871e1fd81c86d3627dda2ac8
> >>Author: WANG Cong <xiyou.wangcong@gmail.com>
> >>Date:   Mon Mar 5 15:05:13 2012 -0800
> >>
> >>IIUC, this commit just fixes a bug of counting pgtable entries. As the
> >>result, another problem came up to the surface. In the case of my
> >>machine(16GB memory), before applying 722bc6, find_early_table_space()
> >>requests about 12KB free area and it can be got from 560K@64K area
> >>luckily. I think the size find_early_table_space() requests was a bug.
> >>After the bug is fixed by the commit 722bc6, find_early_table_space()
> >>requires 1.8MB area and it fails as I wrote.
> >
> >Thanks for tracking this, Takao!
> >
> >I bet you are using x86_64 not x86 PAE? If so, could you try this patch
> >https://patchwork.kernel.org/patch/1195751/
> >? I already reviewed it.
> 
> Great, I applied it and now kdump works. Thanks!

Did something happen on this patch. We definitely want to gain back the
capability to be able to reserve 512MB of kdump memory.

Thanks
Vivek

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