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SubjectRe: [Patch 8/8] kexec: allow to shrink reserved memory
Eric W. Biederman wrote:
> Amerigo Wang <amwang@redhat.com> writes:
>
>
>>>
>>>
>>>> + ret = kexec_crash_image != NULL;
>>>> + mutex_unlock(&kexec_mutex);
>>>> + return ret;
>>>> +}
>>>> +
>>>> +size_t get_crash_memory_size(void)
>>>> +{
>>>> + size_t size;
>>>> + if (!mutex_trylock(&kexec_mutex))
>>>> + return 1;
>>>>
>>>>
>>> We don't need trylock on this code path
>>>
>>>
>>>
>> Hmm, crashk_res is a global struct, so other process can also
>> change it... but currently no process does that, right?
>>
>>
>
> We still need the lock. Just doing trylock doesn't instead
> of just sleeping doesn't seem to make any sense on these
> code paths.
>
>

Ok, got it.

>>>
>>>
>>>> + start = crashk_res.start;
>>>> + end = crashk_res.end;
>>>> +
>>>> + if (new_size >= end - start + 1) {
>>>> + ret = -EINVAL;
>>>> + if (new_size == end - start + 1)
>>>> + ret = 0;
>>>> + goto unlock;
>>>> + }
>>>> +
>>>> + start = roundup(start, PAGE_SIZE);
>>>> + end = roundup(start + new_size, PAGE_SIZE) - 1;
>>>> + npages = (end + 1 - start ) / PAGE_SIZE;
>>>> +
>>>> + pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
>>>> + if (!pages) {
>>>> + ret = -ENOMEM;
>>>> + goto unlock;
>>>> + }
>>>> + for (i = 0; i < npages; i++) {
>>>> + addr = end + 1 + i * PAGE_SIZE;
>>>> + pages[i] = virt_to_page(addr);
>>>> + }
>>>> +
>>>> + vaddr = vm_map_ram(pages, npages, 0, PAGE_KERNEL);
>>>>
>>>>
>>> This is the wrong kernel call to use. I expect this needs to look
>>> like a memory hotplug event. This does not put the pages into the
>>> free page pool.
>>>
>>>
>> Well, I also wanted to use an memory-hotplug API, but that will make the code
>> depend on memory-hotplug, which certainly is not what we want...
>>
>> I checked the mm code, actually what I need is an API which is similar to
>> add_active_range(), but add_active_range() can't be used here since it is marked
>> as "__init".
>>
>> Do we have that kind of API in mm? I can't find one.
>>
>
> Perhaps we will need to remove __init from add_active_range. I know the logic
> but I'm not up to speed on the mm pieces at the moment.
>

Not that simple, marking it as "__init" means it uses some "__init" data
which will be dropped after initialization.

Thanks.



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