linux-kernel - Re: [PATCH v1 5/5] mm/memory_hotplug: print only with DEBUG_VM in online/offline

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Date:   Mon, 20 Aug 2018 11:49:20 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...hadventures.net>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Kemi Wang <kemi.wang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Jia He <jia.he@...-semitech.com>,
        Oscar Salvador <osalvador@...e.de>,
        Petr Tesarik <ptesarik@...e.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mathieu Malaterre <malat@...ian.org>,
        Baoquan He <bhe@...hat.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Ross Zwisler <zwisler@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v1 5/5] mm/memory_hotplug: print only with DEBUG_VM in
 online/offline_pages()

On 20.08.2018 11:45, David Hildenbrand wrote:
> On 17.08.2018 10:18, Oscar Salvador wrote:
>>>  failed_addition:
>>> +#ifdef CONFIG_DEBUG_VM
>>>  	pr_debug("online_pages [mem %#010llx-%#010llx] failed\n",
>>>  		 (unsigned long long) pfn << PAGE_SHIFT,
>>>  		 (((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);
>>> +#endif
>>
>> I have never been sure about this.
>> IMO, if I fail to online pages, I want to know I failed.
>> I think that pr_err would be better than pr_debug and without CONFIG_DEBUG_VM.
> 
> I consider both error messages only partially useful, as
> 
> 1. They only catch a subset of actual failures the function handles.
>    E.g. onlining will not report an error message if the memory notifier
>    failed.

That statement was wrong. It is rather in offline_pages, errors from
start_isolate_page_range() are ignored.

> 2. Onlining/Offlining is usually (with exceptions - e.g. onlining during
>    add_memory) triggered from user space, where we present an error
>    code. At any times, the actual state of the memory blocks can be
>    observed by querying the state.
> 
> I would even vote for dropping the two error case messages completely.
> At least I don't consider them very useful.
> 
>>
>> But at least, if not, envolve it with a CONFIG_DEBUG_VM, but change pr_debug to pr_info.
>>
>>> +#ifdef CONFIG_DEBUG_VM
>>>  	pr_debug("memory offlining [mem %#010llx-%#010llx] failed\n",
>>>  		 (unsigned long long) start_pfn << PAGE_SHIFT,
>>>  		 ((unsigned long long) end_pfn << PAGE_SHIFT) - 1);
>>> +#endif
>>
>> Same goes here.
>>
>> Thanks
>>
> 
> 


-- 

Thanks,

David / dhildenb