linux-kernel - Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in has_unmovable

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Date:   Tue, 14 Jan 2020 16:33:19 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...nel.org>
Cc:     David Hildenbrand <david@...hat.com>, Qian Cai <cai@....pw>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        linux-kernel@...r.kernel.org, Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH] mm/page_alloc: Add a reason for reserved pages in
 has_unmovable_pages()



On 01/14/2020 03:53 PM, 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?

This looks better than what we have right now though my initial thought
was similar to what Michal had suggested earlier.

> 
> 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,
> 
>