linux-kernel - Re: [PATCH] mm/debug:

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Date:   Mon, 11 Nov 2019 15:41:37 -0800
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/debug:


On 11/11/19 3:02 PM, Andrew Morton wrote:
> On Mon, 11 Nov 2019 14:49:35 -0800 Ralph Campbell <rcampbell@...dia.com> wrote:
> 
>> When dumping struct page information, __dump_page() prints the page type
>> with a trailing blank followed by the page flags on a separate line:
>>
>> anon
>> flags: 0x100000000090034(uptodate|lru|active|head|swapbacked)
>>
>> Fix this by using pr_cont() instead of pr_warn() to get a single line:
>>
>> anon flags: 0x100000000090034(uptodate|lru|active|head|swapbacked)
>>
>> Signed-off-by: Ralph Campbell <rcampbell@...dia.com>
>> ---
>>   mm/debug.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/debug.c b/mm/debug.c
>> index 8345bb6e4769..752c78721ea0 100644
>> --- a/mm/debug.c
>> +++ b/mm/debug.c
>> @@ -87,7 +87,7 @@ void __dump_page(struct page *page, const char *reason)
>>   	}
>>   	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
>>   
>> -	pr_warn("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>> +	pr_cont("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>>   
>>   hex_only:
>>   	print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32,
> 
> This is the case if PageAnon || PageKsm || mapping.  If it is, say,
> PageSlab then we effectively do
> 
> 	pr_warn("stuff-with-no-newline");
> 	pr_cont("\n");
> 	pr_cont("flags: ...\n");
> 
> does this work OK?  what facility level will that "flags: " line get?

I don't see a "\n" in the "mapping" case but the
	if (mapping->host && mapping->host->i_dentry.first)
		pr_warn("name:\"%pd\" ", dentry)
would end up on a new line.
Ugh. I guess the dentry name could be fairly long.
I guess I will just convert to using "\n".

AFAIK, there is no locking between pr_warn() and pr_cont() so the latter
could get appended to any facility level. But that isn't a problem I
plan to fix.