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 at 64K memmap=130492K at 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 at 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 at 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. Sorry for the trouble!
