linux-kernel - Re: [PATCH v2 1/7] mm/compaction: split freepages without holding the zone lock

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Date:	Fri, 3 Jun 2016 12:10:10 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:	mgorman@...hsingularity.net, Minchan Kim <minchan@...nel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 1/7] mm/compaction: split freepages without holding the
 zone lock

On 05/26/2016 04:37 AM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....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@....com>

So it wasn't possible to at least move this code from compaction.c to 
page_alloc.c? Or better, reuse prep_new_page() with some forged gfp/alloc_flags? 
As we discussed in v1...

> ---
>  include/linux/mm.h |  1 -
>  mm/compaction.c    | 42 ++++++++++++++++++++++++++++++------------
>  mm/page_alloc.c    | 27 ---------------------------
>  3 files changed, 30 insertions(+), 40 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a00ec81..1a1782c 100644
> --- 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 1427366..8e013eb 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);
> +
> +		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);
>
> -	list_for_each_entry(page, list, lru) {
> -		arch_alloc_page(page, 0);
> -		kernel_map_pages(page, 1, 1);
> -		kasan_alloc_pages(page, 0);
> +		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)
> @@ -368,12 +386,13 @@ 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;
>
>  		/*
> @@ -439,13 +458,12 @@ 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, page_order(page));
> +		set_page_private(page, order);
>  		total_isolated += isolated;
> -		for (i = 0; i < isolated; i++) {
> -			list_add(&page->lru, freelist);
> -			page++;
> -		}
> +		list_add_tail(&page->lru, freelist);
>
>  		/* If a page was split, advance to the end of it */
>  		if (isolated) {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d27e8b9..5134f46 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2525,33 +2525,6 @@ 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.
>