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Subject: Re: [PATCH v1 5/5] mm/memory_hotplug: print only with DEBUG_VM in
 online/offline_pages()
To:     Oscar Salvador <osalvador@techadventures.net>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@oracle.com>,
        Kemi Wang <kemi.wang@intel.com>,
        David Rientjes <rientjes@google.com>,
        Jia He <jia.he@hxt-semitech.com>,
        Oscar Salvador <osalvador@suse.de>,
        Petr Tesarik <ptesarik@suse.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Mathieu Malaterre <malat@debian.org>,
        Baoquan He <bhe@redhat.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Ross Zwisler <zwisler@kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
References: <20180816100628.26428-1-david@redhat.com>
 <20180816100628.26428-6-david@redhat.com>
 <20180817081853.GB17638@techadventures.net>
From:   David Hildenbrand <david@redhat.com>
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Message-ID: <6f52b600-06be-8b30-d181-04489fa6e9f2@redhat.com>
Date:   Mon, 20 Aug 2018 11:45:46 +0200
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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.
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