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SubjectRe: [PACTH v9] stacktrace: Eliminate task stack trace duplication
On Tue, Aug 16, 2016 at 07:12:36PM -0400, robert.foss@collabora.com wrote:
> From: Ying Han <yinghan@google.com>
>
> The problem with small dmesg ring buffer like 512k is that only limited number
> of task traces will be logged. Sometimes we lose important information only
> because of too many duplicated stack traces. This problem occurs when dumping
> lots of stacks in a single operation, such as sysrq-T.
>
> This patch tries to reduce the duplication of task stack trace in the dump
> message by hashing the task stack. The hashtable is a 32k pre-allocated buffer
> during bootup. Each time if we find the identical task trace in the task stack,
> we dump only the pid of the task which has the task trace dumped. So it is easy
> to back track to the full stack with the pid.
>
> When we do the hashing, we eliminate garbage entries from stack traces. Those
> entries are still being printed in the dump to provide more debugging
> informations.
>
> [ 53.510162] kworker/0:0 S ffffffff8161d820 0 4 2 0x00000000
> [ 53.517237] ffff88027547de60 0000000000000046 ffffffff812ab840 0000000000000000
> [ 53.524663] ffff880275460080 ffff88027547dfd8 ffff88027547dfd8 ffff88027547dfd8
> [ 53.532092] ffffffff81813020 ffff880275460080 0000000000000000 ffff8808758670c0
> [ 53.539521] Call Trace:
> [ 53.541974] [<ffffffff812ab840>] ? cfq_init_queue+0x350/0x350
> [ 53.547791] [<ffffffff81524d49>] schedule+0x29/0x70
> [ 53.552761] [<ffffffff810945a3>] worker_thread+0x233/0x380
> [ 53.558318] [<ffffffff81094370>] ? manage_workers.isra.28+0x230/0x230
> [ 53.564839] [<ffffffff81099a73>] kthread+0x93/0xa0
> [ 53.569714] [<ffffffff8152e6d4>] kernel_thread_helper+0x4/0x10
> [ 53.575628] [<ffffffff810999e0>] ? kthread_worker_fn+0x140/0x140
> [ 53.581714] [<ffffffff8152e6d0>] ? gs_change+0xb/0xb
> [ 53.586762] kworker/u:0 S ffffffff8161d820 0 5 2 0x00000000
> [ 53.593858] ffff88027547fe60 0000000000000046 ffffffffa005cc70 0000000000000000
> [ 53.601307] ffff8802754627d0 ffff88027547ffd8 ffff88027547ffd8 ffff88027547ffd8
> [ 53.608788] ffffffff81813020 ffff8802754627d0 0000000000011fc0 ffff8804758670c0
> [ 53.616232] Call Trace:
> [ 53.618676] <Same stack as pid 4>
>

You might want to wait a bit and have a look at this:

https://lkml.kernel.org/r/cover.1471011425.git.jpoimboe@redhat.com

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