linux-kernel - Re: [RFC PATCH 2/5] mm: lower the printk loglevel for __dump

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Date:   Fri, 16 Nov 2018 08:56:34 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <OSalvador@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH 2/5] mm: lower the printk loglevel for __dump_page
 messages

On 11/07/18 at 11:18am, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> __dump_page messages use KERN_EMERG resp. KERN_ALERT loglevel (this is
> the case since 2004). Most callers of this function are really detecting
> a critical page state and BUG right after. On the other hand the
> function is called also from contexts which just want to inform about
> the page state and those would rather not disrupt logs that much (e.g.
> some systems route these messages to the normal console).
> 
> Reduce the loglevel to KERN_WARNING to make dump_page easier to reuse
> for other contexts while those messages will still make it to the kernel
> log in most setups. Even if the loglevel setup filters warnings away
> those paths that are really critical already print the more targeted
> error or panic and that should make it to the kernel log.
> 
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/debug.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/debug.c b/mm/debug.c
> index a33177bfc856..d18c5cea3320 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -54,7 +54,7 @@ void __dump_page(struct page *page, const char *reason)
>  	 * dump_page() when detected.
>  	 */
>  	if (page_poisoned) {
> -		pr_emerg("page:%px is uninitialized and poisoned", page);
> +		pr_warn("page:%px is uninitialized and poisoned", page);
>  		goto hex_only;
>  	}
>  
> @@ -65,27 +65,27 @@ void __dump_page(struct page *page, const char *reason)
>  	 */
>  	mapcount = PageSlab(page) ? 0 : page_mapcount(page);
>  
> -	pr_emerg("page:%px count:%d mapcount:%d mapping:%px index:%#lx",
> +	pr_warn("page:%px count:%d mapcount:%d mapping:%px index:%#lx",
	pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx",

Better print it as refcount since we have renamed it. 

>  		  page, page_ref_count(page), mapcount,
>  		  page->mapping, page_to_pgoff(page));
>  	if (PageCompound(page))
>  		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
>  	pr_cont("\n");
>  	if (PageAnon(page))
> -		pr_emerg("anon ");
> +		pr_warn("anon ");
>  	else if (PageKsm(page))
> -		pr_emerg("ksm ");
> +		pr_warn("ksm ");
>  	else if (mapping) {
> -		pr_emerg("%ps ", mapping->a_ops);
> +		pr_warn("%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);
> +			pr_warn("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);
> +	pr_warn("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>  
>  hex_only:
>  	print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE, 32,
> @@ -93,11 +93,11 @@ void __dump_page(struct page *page, const char *reason)
>  			sizeof(struct page), false);
>  
>  	if (reason)
> -		pr_alert("page dumped because: %s\n", reason);
> +		pr_warn("page dumped because: %s\n", reason);
>  
>  #ifdef CONFIG_MEMCG
>  	if (!page_poisoned && page->mem_cgroup)
> -		pr_alert("page->mem_cgroup:%px\n", page->mem_cgroup);
> +		pr_warn("page->mem_cgroup:%px\n", page->mem_cgroup);
>  #endif
>  }
>  
> -- 
> 2.19.1
>