Re: [PATCH v2] mm: page_alloc: dump migrate-failed pages

[Andrew Morton <akpm@linux-foundation.org>]

On Mon,  8 Mar 2021 12:20:47 -0800 Minchan Kim <minchan@kernel.org> wrote:

> alloc_contig_range is usually used on cma area or movable zone.
> It's critical if the page migration fails on those areas so
> dump more debugging message.
> 
> page refcount, mapcount with page flags on dump_page are
> helpful information to deduce the culprit. Furthermore,
> dump_page_owner was super helpful to find long term pinner
> who initiated the page allocation.
> 
> Admin could enable the dump like this(by default, disabled)
> 
> 	echo "func dump_migrate_failure_pages +p" > control
> 
> Admin could disable it.
> 
> 	echo "func dump_migrate_failure_pages =_" > control
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8453,6 +8453,34 @@ static unsigned long pfn_max_align_up(unsigned long pfn)
>  				pageblock_nr_pages));
>  }
>  
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
> +static DEFINE_RATELIMIT_STATE(alloc_contig_ratelimit_state,
> +		DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST);
> +int alloc_contig_ratelimit(void)
> +{
> +	return __ratelimit(&alloc_contig_ratelimit_state);
> +}

Wow, that's an eyesore.  We're missing helpers in the ratelimit code. 
Can we do something like

/* description goes here */
#define RATELIMIT2(interval, burst)
({
	static DEFINE_RATELIMIT_STATE(_rs, interval, burst);

	__ratelimit(_rs);
})

#define RATELIMIT()
	RATELIMIT2(DEFAULT_RATELIMIT_INTERVAL, DEFAULT_RATELIMIT_BURST)

> +void dump_migrate_failure_pages(struct list_head *page_list)
> +{
> +	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor,
> +			"migrate failure");
> +	if (DYNAMIC_DEBUG_BRANCH(descriptor) &&
> +			alloc_contig_ratelimit()) {
> +		struct page *page;
> +
> +		WARN(1, "failed callstack");
> +		list_for_each_entry(page, page_list, lru)
> +			dump_page(page, "migration failure");
> +	}
> +}

Then we can simply do

	if (DYNAMIC_DEBUG_BRANCH(descriptor) && RATELIMIT())