Re: [patch] mm, compaction: abort free scanner if split fails

[Vlastimil Babka <vbabka@suse.cz>]

On 06/23/2016 01:40 AM, David Rientjes wrote:
> On Wed, 22 Jun 2016, Andrew Morton wrote:
>
>> And
>> mm-compaction-split-freepages-without-holding-the-zone-lock-fix.patch
>> churns things around some more.  Now this:
>>
>>
>> 		/* Found a free page, will break it into order-0 pages */
>> 		order = page_order(page);
>> 		isolated = __isolate_free_page(page, order);
>> 		set_page_private(page, order);
>> 		total_isolated += isolated;
>> 		list_add_tail(&page->lru, freelist);
>> 		cc->nr_freepages += isolated;
>> 		if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
>> 			blockpfn += isolated;
>> 			break;
>> 		}
>> 		/* Advance to the end of split page */
>> 		blockpfn += isolated - 1;
>> 		cursor += isolated - 1;
>> 		continue;
>>
>> isolate_fail:
>>
>> and things are looking a bit better...
>>
>
> This looks like it's missing the
>
> 	if (!isolated)
> 		break;
>
> check from mm-compaction-abort-free-scanner-if-split-fails.patch which is
> needed to properly terminate when the low watermark fails (and adding to
> freelist as Minchan mentioned before I saw this patch).

Agreed.

>
> I rebased
> mm-compaction-split-freepages-without-holding-the-zone-lock.patch as I
> thought it should be done and folded
> mm-compaction-split-freepages-without-holding-the-zone-lock-fix.patch into
> it for simplicity.  I think this should replace
> mm-compaction-split-freepages-without-holding-the-zone-lock.patch in -mm.

Yes, it should replace both the .patch and the -fix.patch.

Thanks!

>
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
>
> We don't need to split freepages with holding the zone lock.  It will
> cause more contention on zone lock so not desirable.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -537,7 +537,6 @@ void __put_page(struct page *page);
>  void put_pages_list(struct list_head *pages);
>
>  void split_page(struct page *page, unsigned int order);
> -int split_free_page(struct page *page);
>
>  /*
>   * Compound pages have a destructor function.  Provide a
> diff --git a/mm/compaction.c b/mm/compaction.c
> index ab21497..9d17b21 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -65,13 +65,31 @@ static unsigned long release_freepages(struct list_head *freelist)
>
>  static void map_pages(struct list_head *list)
>  {
> -	struct page *page;
> +	unsigned int i, order, nr_pages;
> +	struct page *page, *next;
> +	LIST_HEAD(tmp_list);
> +
> +	list_for_each_entry_safe(page, next, list, lru) {
> +		list_del(&page->lru);
>
> -	list_for_each_entry(page, list, lru) {
> -		arch_alloc_page(page, 0);
> -		kernel_map_pages(page, 1, 1);
> -		kasan_alloc_pages(page, 0);
> +		order = page_private(page);
> +		nr_pages = 1 << order;
> +		set_page_private(page, 0);
> +		set_page_refcounted(page);
> +
> +		arch_alloc_page(page, order);
> +		kernel_map_pages(page, nr_pages, 1);
> +		kasan_alloc_pages(page, order);
> +		if (order)
> +			split_page(page, order);
> +
> +		for (i = 0; i < nr_pages; i++) {
> +			list_add(&page->lru, &tmp_list);
> +			page++;
> +		}
>  	}
> +
> +	list_splice(&tmp_list, list);
>  }
>
>  static inline bool migrate_async_suitable(int migratetype)
> @@ -406,12 +424,13 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>  	unsigned long flags = 0;
>  	bool locked = false;
>  	unsigned long blockpfn = *start_pfn;
> +	unsigned int order;
>
>  	cursor = pfn_to_page(blockpfn);
>
>  	/* Isolate free pages. */
>  	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
> -		int isolated, i;
> +		int isolated;
>  		struct page *page = cursor;
>
>  		/*
> @@ -477,17 +496,17 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>  				goto isolate_fail;
>  		}
>
> -		/* Found a free page, break it into order-0 pages */
> -		isolated = split_free_page(page);
> +		/* Found a free page, will break it into order-0 pages */
> +		order = page_order(page);
> +		isolated = __isolate_free_page(page, order);
>  		if (!isolated)
>  			break;
> +		set_page_private(page, order);
>
>  		total_isolated += isolated;
>  		cc->nr_freepages += isolated;
> -		for (i = 0; i < isolated; i++) {
> -			list_add(&page->lru, freelist);
> -			page++;
> -		}
> +		list_add_tail(&page->lru, freelist);
> +
>  		if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
>  			blockpfn += isolated;
>  			break;
> @@ -606,7 +625,7 @@ isolate_freepages_range(struct compact_control *cc,
>  		 */
>  	}
>
> -	/* split_free_page does not map the pages */
> +	/* __isolate_free_page() does not map the pages */
>  	map_pages(&freelist);
>
>  	if (pfn < end_pfn) {
> @@ -1113,7 +1132,7 @@ static void isolate_freepages(struct compact_control *cc)
>  		}
>  	}
>
> -	/* split_free_page does not map the pages */
> +	/* __isolate_free_page() does not map the pages */
>  	map_pages(freelist);
>
>  	/*
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2560,33 +2560,6 @@ int __isolate_free_page(struct page *page, unsigned int order)
>  }
>
>  /*
> - * Similar to split_page except the page is already free. As this is only
> - * being used for migration, the migratetype of the block also changes.
> - * As this is called with interrupts disabled, the caller is responsible
> - * for calling arch_alloc_page() and kernel_map_page() after interrupts
> - * are enabled.
> - *
> - * Note: this is probably too low level an operation for use in drivers.
> - * Please consult with lkml before using this in your driver.
> - */
> -int split_free_page(struct page *page)
> -{
> -	unsigned int order;
> -	int nr_pages;
> -
> -	order = page_order(page);
> -
> -	nr_pages = __isolate_free_page(page, order);
> -	if (!nr_pages)
> -		return 0;
> -
> -	/* Split into individual pages */
> -	set_page_refcounted(page);
> -	split_page(page, order);
> -	return nr_pages;
> -}
> -
> -/*
>   * Update NUMA hit/miss statistics
>   *
>   * Must be called with interrupts disabled.
>