linux-kernel - Re: [PATCH 1/5] mm: print more information about mapping in __dump

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Date:   Fri, 16 Nov 2018 17:25:56 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Oscar Salvador <OSalvador@...e.com>, Baoquan He <bhe@...hat.com>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 1/5] mm: print more information about mapping in
 __dump_page



On 11/16/2018 02:00 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> __dump_page prints the mapping pointer but that is quite unhelpful
> for many reports because the pointer itself only helps to distinguish
> anon/ksm mappings from other ones (because of lowest bits
> set). Sometimes it would be much more helpful to know what kind of
> mapping that is actually and if we know this is a file mapping then also
> try to resolve the dentry name.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/debug.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index cdacba12e09a..a33177bfc856 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -44,6 +44,7 @@ const struct trace_print_flags vmaflag_names[] = {
>  
>  void __dump_page(struct page *page, const char *reason)
>  {
> +	struct address_space *mapping = page_mapping(page);
>  	bool page_poisoned = PagePoisoned(page);
>  	int mapcount;
>  
> @@ -70,6 +71,18 @@ void __dump_page(struct page *page, const char *reason)
>  	if (PageCompound(page))
>  		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
>  	pr_cont("\n");
> +	if (PageAnon(page))
> +		pr_emerg("anon ");
> +	else if (PageKsm(page))
> +		pr_emerg("ksm ");
> +	else if (mapping) {
> +		pr_emerg("%ps ", mapping->a_ops);
> +		if (mapping->host->i_dentry.first) {
> +			struct dentry *dentry;
> +			dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias);
> +			pr_emerg("name:\"%*s\" ", dentry->d_name.len, dentry->d_name.name);
> +		}
> +	}
>  	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
>  
>  	pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);
> 

Differentiating between anon, ksm mapping and going till dentry information
for file mappings is surely an improvement. 

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>