Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages

From	zhong jiang <zhongjiang@huawei.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages
Date	2016-12-09 07:00 +0100
Message-ID	<sMmnY-7Ru-3@gated-at.bofh.it> (permalink)
References	<sLWWt-7M-7@gated-at.bofh.it> <sM3uW-4u1-5@gated-at.bofh.it> <sMlLc-7BJ-29@gated-at.bofh.it> <sMlUR-7HU-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 2016/12/9 13:19, Eric W. Biederman wrote:
> zhong jiang <zhongjiang@huawei.com> writes:
>
>> On 2016/12/8 17:41, Xunlei Pang wrote:
>>> On 12/08/2016 at 10:37 AM, zhongjiang wrote:
>>>> From: zhong jiang <zhongjiang@huawei.com>
>>>>
> [snip]
>>>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>>>> index 5616755..bfc9621 100644
>>>> --- a/kernel/kexec_core.c
>>>> +++ b/kernel/kexec_core.c
>>>> @@ -441,6 +441,8 @@ static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
>>>>  	while (hole_end <= crashk_res.end) {
>>>>  		unsigned long i;
>>>>  
>>>> +		cond_resched();
>>>> +
>>> I can't see why it would take a long time to loop inside, the job it does is simply to find a control area
>>> not overlapped with image->segment[], you can see the loop "for (i = 0; i < image->nr_segments; i++)",
>>> @hole_end will be advanced to the end of its next nearby segment once overlap was detected each loop,
>>> also there are limited (<=16) segments, so it won't take long to locate the right area.
>>>
>>> Am I missing something?
>>>
>>> Regards,
>>> Xunlei
>>   if the crashkernel = auto is set in cmdline.  it represent crashk_res.end will exceed to 4G, the first allocate control pages will
>>   loop  million times. if we set crashk_res.end to the higher value
>>   manually,  you can image....
> Or in short the cond_resched is about keeping things reasonable when the
> loop has worst case behavior.
>
> Eric
>
>
  Yes,   Thank you reply and comment.

  Regards,
  zhongjiang

Thread

[PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages zhongjiang <zhongjiang@huawei.com> - 2016-12-08 03:50 +0100
  Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages ebiederm@xmission.com (Eric W. Biederman) - 2016-12-08 04:30 +0100
  Re: [PATCH v2] kexec: add cond_resched into  kimage_alloc_crash_control_pages Xunlei Pang <xpang@redhat.com> - 2016-12-08 10:50 +0100
    Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages zhong jiang <zhongjiang@huawei.com> - 2016-12-09 06:20 +0100
      Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages ebiederm@xmission.com (Eric W. Biederman) - 2016-12-09 06:30 +0100
        Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages zhong jiang <zhongjiang@huawei.com> - 2016-12-09 07:00 +0100
      Re: [PATCH v2] kexec: add cond_resched into  kimage_alloc_crash_control_pages Xunlei Pang <xpang@redhat.com> - 2016-12-09 08:20 +0100

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