Re: [RFC PATCH] mm/hotplug: enable memory hotplug for non-lru movable pages

[Yisheng Xie <xieyisheng1@huawei.com>]

hi,
sorry to disturb, I will send another version to make a minor change
about page_lock checking in scan_movable_pages.

On 2017/1/25 11:25, Yisheng Xie wrote:
> We had considered all of the non-lru pages as unmovable before
> commit bda807d44454 ("mm: migrate: support non-lru movable page
> migration"). But now some of non-lru pages like zsmalloc,
> virtio-balloon pages also become movable. So we can offline such
> blocks by using non-lru page migration.
> 
> This patch straightforwardly add non-lru migration code, which
> means adding non-lru related code to the functions which scan
> over pfn and collect pages to be migrated and isolate them before
> migration.
> 
> Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
> ---
>  mm/memory_hotplug.c | 32 +++++++++++++++++++++-----------
>  mm/page_alloc.c     |  8 ++++++--
>  2 files changed, 27 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e43142c1..fbdbffc 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1510,15 +1510,16 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn)
>  }
>  
>  /*
> - * Scan pfn range [start,end) to find movable/migratable pages (LRU pages
> - * and hugepages). We scan pfn because it's much easier than scanning over
> - * linked list. This function returns the pfn of the first found movable
> - * page if it's found, otherwise 0.
> + * Scan pfn range [start,end) to find movable/migratable pages (LRU pages,
> + * non-lru movable pages and hugepages). We scan pfn because it's much
> + * easier than scanning over linked list. This function returns the pfn
> + * of the first found movable page if it's found, otherwise 0.
>   */
>  static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>  {
>  	unsigned long pfn;
>  	struct page *page;
> +	bool movable;
>  	for (pfn = start; pfn < end; pfn++) {
>  		if (pfn_valid(pfn)) {
>  			page = pfn_to_page(pfn);
> @@ -1531,6 +1532,11 @@ static unsigned long scan_movable_pages(unsigned long start, unsigned long end)
>  					pfn = round_up(pfn + 1,
>  						1 << compound_order(page)) - 1;
>  			}
> +			lock_page(page);
> +			movable = __PageMovable(page);
> +			unlock_page(page);
> +			if (movable)
> +				return pfn;
>  		}
>  	}
>  	return 0;
> @@ -1600,21 +1606,25 @@ static struct page *new_node_page(struct page *page, unsigned long private,
>  		if (!get_page_unless_zero(page))
>  			continue;
>  		/*
> -		 * We can skip free pages. And we can only deal with pages on
> -		 * LRU.
> +		 * We can skip free pages. And we can deal with pages on
> +		 * LRU and non-lru movable pages.
>  		 */
> -		ret = isolate_lru_page(page);
> +		if (PageLRU(page))
> +			ret = isolate_lru_page(page);
> +		else
> +			ret = !isolate_movable_page(page, ISOLATE_UNEVICTABLE);
>  		if (!ret) { /* Success */
>  			put_page(page);
>  			list_add_tail(&page->lru, &source);
>  			move_pages--;
> -			inc_node_page_state(page, NR_ISOLATED_ANON +
> -					    page_is_file_cache(page));
> +			if (!__PageMovable(page))
> +				inc_node_page_state(page, NR_ISOLATED_ANON +
> +						    page_is_file_cache(page));
>  
>  		} else {
>  #ifdef CONFIG_DEBUG_VM
> -			pr_alert("removing pfn %lx from LRU failed\n", pfn);
> -			dump_page(page, "failed to remove from LRU");
> +			pr_alert("failed to isolate pfn %lx\n", pfn);
> +			dump_page(page, "isolation failed");
>  #endif
>  			put_page(page);
>  			/* Because we don't have big zone->lock. we should
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d604d25..52d3067 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7055,8 +7055,9 @@ void *__init alloc_large_system_hash(const char *tablename,
>   * If @count is not zero, it is okay to include less @count unmovable pages
>   *
>   * PageLRU check without isolation or lru_lock could race so that
> - * MIGRATE_MOVABLE block might include unmovable pages. It means you can't
> - * expect this function should be exact.
> + * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable
> + * check without lock_page also may miss some movable non-lru pages at
> + * race condition. So you can't expect this function should be exact.
>   */
>  bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  			 bool skip_hwpoisoned_pages)
> @@ -7112,6 +7113,9 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  		if (skip_hwpoisoned_pages && PageHWPoison(page))
>  			continue;
>  
> +		if (__PageMovable(page))
> +			continue;
> +
>  		if (!PageLRU(page))
>  			found++;
>  		/*
> 

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