Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 09 Dec 2016 18:19:37 +1300 | Subject | Re: [PATCH v2] kexec: add cond_resched into kimage_alloc_crash_control_pages |
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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
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