Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()

From: Ralph Campbell <rcampbell@nvidia.com>
To: Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	David Hildenbrand <david@redhat.com>, Qian Cai <cai@lca.pw>,
	<linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>,
	Oscar Salvador <osalvador@suse.de>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Pavel Tatashin <pavel.tatashin@microsoft.com>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable_pages()
Date: Tue, 14 Jan 2020 10:22:48 -0800	[thread overview]
Message-ID: <958fa7cd-0e88-3387-d4bf-e8bfcfdb256b@nvidia.com> (raw)
In-Reply-To: <20200114113230.GM19428@dhcp22.suse.cz>


On 1/14/20 3:32 AM, Michal Hocko wrote:
> On Tue 14-01-20 11:23:52, Vlastimil Babka wrote:
>> On 1/14/20 10:10 AM, Michal Hocko wrote:
>>> [Cc Ralph]
>>>> The reason is dump_page() does not print page->flags universally
>>>> and only does so for KSM, Anon and File pages while excluding
>>>> reserved pages at boot. Wondering should not we make printing
>>>> page->flags universal ?
>>>
>>> We used to do that and this caught me as a surprise when looking again.
>>> This is a result of 76a1850e4572 ("mm/debug.c: __dump_page() prints an
>>> extra line") which is a cleanup patch and I suspect this result was not
>>> anticipated.
>>>
>>> The following will do the trick but I cannot really say I like the code
>>> duplication. pr_cont in this case sounds like a much cleaner solution to
>>> me.
>>
>> How about this then?
> 
> Yes makes sense as well.
> 
>> diff --git mm/debug.c mm/debug.c
>> index 0461df1207cb..6a52316af839 100644
>> --- mm/debug.c
>> +++ mm/debug.c
>> @@ -47,6 +47,7 @@ void __dump_page(struct page *page, const char *reason)
>>   	struct address_space *mapping;
>>   	bool page_poisoned = PagePoisoned(page);
>>   	int mapcount;
>> +	char *type = "";
>>   
>>   	/*
>>   	 * If struct page is poisoned don't access Page*() functions as that
>> @@ -78,9 +79,9 @@ void __dump_page(struct page *page, const char *reason)
>>   			page, page_ref_count(page), mapcount,
>>   			page->mapping, page_to_pgoff(page));
>>   	if (PageKsm(page))
>> -		pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags);
>> +		type = "ksm ";
>>   	else if (PageAnon(page))
>> -		pr_warn("anon flags: %#lx(%pGp)\n", page->flags, &page->flags);
>> +		type = "anon ";
>>   	else if (mapping) {
>>   		if (mapping->host && mapping->host->i_dentry.first) {
>>   			struct dentry *dentry;
>> @@ -88,10 +89,11 @@ void __dump_page(struct page *page, const char *reason)
>>   			pr_warn("%ps name:\"%pd\"\n", mapping->a_ops, dentry);
>>   		} else
>>   			pr_warn("%ps\n", mapping->a_ops);
>> -		pr_warn("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>>   	}
>>   	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
>>   
>> +	pr_warn("%sflags: %#lx(%pGp)\n", type, page->flags, &page->flags);
>> +
>>   hex_only:
>>   	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
>>   			sizeof(unsigned long), page,
>>
> 
Looks good to me. Thanks for the clean up.
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>