[PATCH v1 3/8] kexec: export PG_offline to VMCOREINFO

David Hildenbrand david at redhat.com
Wed Nov 21 08:50:17 UTC 2018

On 21.11.18 07:04, Baoquan He wrote:
> On 11/19/18 at 11:16am, David Hildenbrand wrote:
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 933cb3e45b98..093c9f917ed0 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -464,6 +464,8 @@ static int __init crash_save_vmcoreinfo_init(void)
>> +#define PAGE_OFFLINE_MAPCOUNT_VALUE	(~PG_offline)
>>  #endif
> This solution looks good to me. One small concern is why we don't
> export PG_offline to vmcoreinfo directly, then define
> PAGE_OFFLINE_MAPCOUNT_VALUE in makedumpfile. We have been exporting
> kernel data/MACRO directly, why this one is exceptional.

1. We are much more similar to PG_buddy (in contrast to actual page
flags), and for PG_buddy it is historically handled like this (and I
think it makes sense to expose these as actual MAPCOUNT_VALUEs).

2. Right now only one page type per page is supported. Therefore only
exactly one value in mapcount indicates e.g. PageBuddy()/PageOffline().

Now, if we ever decide to change this (e.g. treat them like real flags),
it is much easier to switch to PG_offline/PG_buddy then. We can directly
see in makedumpfile that .*_MAPCOUNT_VALUE is no longer available but
instead e.g. PG_offline and PG_buddy. Instead we would no see a change
in makedumpfile and would have to rely on other properties.

If there are no strong opinions I will leave it like this.


> Thanks
> Baoquan



David / dhildenb

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