Linux Virtualization - Mar 2016 - [PATCH v1 13/19] zsmalloc: factor page chain functionality out

On 2016/3/11 15:30, Minchan Kim wrote:
> For migration, we need to create sub-page chain of zspage
> dynamically so this patch factors it out from alloc_zspage.
>
> As a minor refactoring, it makes OBJ_ALLOCATED_TAG assign
> more clear in obj_malloc(it could be another patch but it's
> trivial so I want to put together in this patch).
>
> Signed-off-by: Minchan Kim <minchan at kernel.org>
> ---
>   mm/zsmalloc.c | 78
++++++++++++++++++++++++++++++++++-------------------------
>   1 file changed, 45 insertions(+), 33 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index bfc6a048afac..f86f8aaeb902 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -977,7 +977,9 @@ static void init_zspage(struct size_class *class,
struct page *first_page)
>   	unsigned long off = 0;
>   	struct page *page = first_page;
>
> -	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
> +	first_page->freelist = NULL;
> +	INIT_LIST_HEAD(&first_page->lru);
> +	set_zspage_inuse(first_page, 0);
>
>   	while (page) {
>   		struct page *next_page;
> @@ -1022,13 +1024,44 @@ static void init_zspage(struct size_class *class,
struct page *first_page)
>   	set_freeobj(first_page, 0);
>   }
>
> +static void create_page_chain(struct page *pages[], int nr_pages)
> +{
> +	int i;
> +	struct page *page;
> +	struct page *prev_page = NULL;
> +	struct page *first_page = NULL;
> +
> +	for (i = 0; i < nr_pages; i++) {
> +		page = pages[i];
> +
> +		INIT_LIST_HEAD(&page->lru);
> +		if (i == 0) {
> +			SetPagePrivate(page);
> +			set_page_private(page, 0);
> +			first_page = page;
> +		}
> +
> +		if (i == 1)
> +			set_page_private(first_page, (unsigned long)page);
> +		if (i >= 1)
> +			set_page_private(page, (unsigned long)first_page);
> +		if (i >= 2)
> +			list_add(&page->lru, &prev_page->lru);
> +		if (i == nr_pages - 1)
> +			SetPagePrivate2(page);
> +
> +		prev_page = page;
> +	}
> +}
> +
>   /*
>    * Allocate a zspage for the given size class
>    */
>   static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
>   {
> -	int i, error;
> +	int i;
>   	struct page *first_page = NULL, *uninitialized_var(prev_page);
> +	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE];
>
>   	/*
>   	 * Allocate individual pages and link them together as:
> @@ -1041,43 +1074,23 @@ static struct page *alloc_zspage(struct size_class
*class, gfp_t flags)
	*uninitialized_var(prev_page) in alloc_zspage is not in use more.
>   	 * (i.e. no other sub-page has this flag set) and PG_private_2 to
>   	 * identify the last page.
>   	 */
> -	error = -ENOMEM;
>   	for (i = 0; i < class->pages_per_zspage; i++) {
>   		struct page *page;
>
>   		page = alloc_page(flags);
> -		if (!page)
> -			goto cleanup;
> -
> -		INIT_LIST_HEAD(&page->lru);
> -		if (i == 0) {	/* first page */
> -			page->freelist = NULL;
> -			SetPagePrivate(page);
> -			set_page_private(page, 0);
> -			first_page = page;
> -			set_zspage_inuse(page, 0);
> +		if (!page) {
> +			while (--i >= 0)
> +				__free_page(pages[i]);
> +			return NULL;
>   		}
> -		if (i == 1)
> -			set_page_private(first_page, (unsigned long)page);
> -		if (i >= 1)
> -			set_page_private(page, (unsigned long)first_page);
> -		if (i >= 2)
> -			list_add(&page->lru, &prev_page->lru);
> -		if (i == class->pages_per_zspage - 1)	/* last page */
> -			SetPagePrivate2(page);
> -		prev_page = page;
> +
> +		pages[i] = page;
>   	}
>
> +	create_page_chain(pages, class->pages_per_zspage);
> +	first_page = pages[0];
>   	init_zspage(class, first_page);
>
> -	error = 0; /* Success */
> -
> -cleanup:
> -	if (unlikely(error) && first_page) {
> -		free_zspage(first_page);
> -		first_page = NULL;
> -	}
> -
>   	return first_page;
>   }
>
> @@ -1419,7 +1432,6 @@ static unsigned long obj_malloc(struct size_class
*class,
>   	unsigned long m_offset;
>   	void *vaddr;
>
> -	handle |= OBJ_ALLOCATED_TAG;
>   	obj = get_freeobj(first_page);
>   	objidx_to_page_and_ofs(class, first_page, obj,
>   				&m_page, &m_offset);
> @@ -1429,10 +1441,10 @@ static unsigned long obj_malloc(struct size_class
*class,
>   	set_freeobj(first_page, link->next >> OBJ_ALLOCATED_TAG);
>   	if (!class->huge)
>   		/* record handle in the header of allocated chunk */
> -		link->handle = handle;
> +		link->handle = handle | OBJ_ALLOCATED_TAG;
>   	else
>   		/* record handle in first_page->private */
> -		set_page_private(first_page, handle);
> +		set_page_private(first_page, handle | OBJ_ALLOCATED_TAG);
>   	kunmap_atomic(vaddr);
>   	mod_zspage_inuse(first_page, 1);
>   	zs_stat_inc(class, OBJ_USED, 1);
>

On Sat, Mar 12, 2016 at 11:09:36AM +0800, xuyiping
wrote:
> 
> 
> On 2016/3/11 15:30, Minchan Kim wrote:
> >For migration, we need to create sub-page chain of zspage
> >dynamically so this patch factors it out from alloc_zspage.
> >
> >As a minor refactoring, it makes OBJ_ALLOCATED_TAG assign
> >more clear in obj_malloc(it could be another patch but it's
> >trivial so I want to put together in this patch).
> >
> >Signed-off-by: Minchan Kim <minchan at kernel.org>
> >---
> >  mm/zsmalloc.c | 78
++++++++++++++++++++++++++++++++++-------------------------
> >  1 file changed, 45 insertions(+), 33 deletions(-)
> >
> >diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> >index bfc6a048afac..f86f8aaeb902 100644
> >--- a/mm/zsmalloc.c
> >+++ b/mm/zsmalloc.c
> >@@ -977,7 +977,9 @@ static void init_zspage(struct size_class *class,
struct page *first_page)
> >  	unsigned long off = 0;
> >  	struct page *page = first_page;
> >
> >-	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
> >+	first_page->freelist = NULL;
> >+	INIT_LIST_HEAD(&first_page->lru);
> >+	set_zspage_inuse(first_page, 0);
> >
> >  	while (page) {
> >  		struct page *next_page;
> >@@ -1022,13 +1024,44 @@ static void init_zspage(struct size_class
*class, struct page *first_page)
> >  	set_freeobj(first_page, 0);
> >  }
> >
> >+static void create_page_chain(struct page *pages[], int nr_pages)
> >+{
> >+	int i;
> >+	struct page *page;
> >+	struct page *prev_page = NULL;
> >+	struct page *first_page = NULL;
> >+
> >+	for (i = 0; i < nr_pages; i++) {
> >+		page = pages[i];
> >+
> >+		INIT_LIST_HEAD(&page->lru);
> >+		if (i == 0) {
> >+			SetPagePrivate(page);
> >+			set_page_private(page, 0);
> >+			first_page = page;
> >+		}
> >+
> >+		if (i == 1)
> >+			set_page_private(first_page, (unsigned long)page);
> >+		if (i >= 1)
> >+			set_page_private(page, (unsigned long)first_page);
> >+		if (i >= 2)
> >+			list_add(&page->lru, &prev_page->lru);
> >+		if (i == nr_pages - 1)
> >+			SetPagePrivate2(page);
> >+
> >+		prev_page = page;
> >+	}
> >+}
> >+
> >  /*
> >   * Allocate a zspage for the given size class
> >   */
> >  static struct page *alloc_zspage(struct size_class *class, gfp_t
flags)
> >  {
> >-	int i, error;
> >+	int i;
> >  	struct page *first_page = NULL, *uninitialized_var(prev_page);
> >+	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE];
> >
> >  	/*
> >  	 * Allocate individual pages and link them together as:
> >@@ -1041,43 +1074,23 @@ static struct page *alloc_zspage(struct
size_class *class, gfp_t flags)
> 
> 	*uninitialized_var(prev_page) in alloc_zspage is not in use more.
True.
It says why we should avoid uninitialized_var if possible.
If we didn't use uninitialized_var, compiler could warn about it
when I did build test.

Thanks.