Re: [PATCH 4/4] thp: increase split_huge_page() success rate

[Vlastimil Babka <vbabka@suse.cz>]

On 12/29/2015 09:57 PM, Kirill A. Shutemov wrote:
> On Mon, Dec 28, 2015 at 03:30:26PM -0800, Andrew Morton wrote:
>> Fair enough.
>>
>> mlocked pages are rare and lru_add_drain() isn't free.  We could easily
>> and cheaply make page_remove_rmap() return "bool was_mlocked" (or,
>> better, "bool might_be_in_lru_cache") to skip this overhead.
>
> Propagating it back is painful. What about this instead:

Looks good.

> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index ecb4ed1a821a..edfa53eda9ca 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3385,6 +3385,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>   	struct page *head = compound_head(page);
>   	struct anon_vma *anon_vma;
>   	int count, mapcount, ret;
> +	bool mlocked;
>
>   	VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
>   	VM_BUG_ON_PAGE(!PageAnon(page), page);
> @@ -3415,11 +3416,13 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>   		goto out_unlock;
>   	}
>
> +	mlocked = PageMlocked(page);
>   	freeze_page(anon_vma, head);
>   	VM_BUG_ON_PAGE(compound_mapcount(head), head);
>
>   	/* Make sure the page is not on per-CPU pagevec as it takes pin */
> -	lru_add_drain();
> +	if (mlocked)
> +		lru_add_drain();
>
>   	/* Prevent deferred_split_scan() touching ->_count */
>   	spin_lock(&split_queue_lock);
>

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