[2/6] mm/swapfile.c: Replace some #ifdef with IS_ENABLED()

Commit Message

Huang, Ying July 12, 2018, 11:36 p.m. UTC

From: Huang Ying <[e-mail]>

In mm/swapfile.c, THP (Transparent Huge Page) swap specific code is
enclosed by #ifdef CONFIG_THP_SWAP/#endif to avoid code dilating when
THP isn't enabled.  But #ifdef/#endif in .c file hurt the code
readability, so Dave suggested to use IS_ENABLED(CONFIG_THP_SWAP)
instead and let compiler to do the dirty job for us.  This has
potential to remove some duplicated code too.  From output of `size`,

		text	   data	    bss	    dec	    hex	filename
THP=y:         26269	   2076	    340	  28685	   700d	mm/swapfile.o
ifdef/endif:   24115	   2028	    340	  26483	   6773	mm/swapfile.o
IS_ENABLED:    24179	   2028	    340	  26547	   67b3	mm/swapfile.o

IS_ENABLED() based solution works quite well, almost as good as that
of #ifdef/#endif.  And from the diffstat, the removed lines are more
than added lines.

One #ifdef for split_swap_cluster() is kept.  Because it is a public
function with a stub implementation for CONFIG_THP_SWAP=n in swap.h.

Signed-off-by: "Huang, Ying" <[e-mail]>
Suggested-by: Dave Hansen <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Shaohua Li <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Daniel Jordan <[e-mail]>
Cc: Dan Williams <[e-mail]>
---
 mm/swapfile.c | 56 ++++++++++++++++----------------------------------------
 1 file changed, 16 insertions(+), 40 deletions(-)

Comments

Daniel Jordan July 13, 2018, 6:38 p.m. UTC | #1

On Fri, Jul 13, 2018 at 07:36:32AM +0800, Huang, Ying wrote:
> @@ -1260,7 +1257,6 @@ static void swapcache_free(swp_entry_t entry)
>  	}
>  }
>  
> -#ifdef CONFIG_THP_SWAP
>  static void swapcache_free_cluster(swp_entry_t entry)
>  {
>  	unsigned long offset = swp_offset(entry);
> @@ -1271,6 +1267,9 @@ static void swapcache_free_cluster(swp_entry_t entry)
>  	unsigned int i, free_entries = 0;
>  	unsigned char val;
>  
> +	if (!IS_ENABLED(CONFIG_THP_SWAP))
> +		return;
> +

VM_WARN_ON_ONCE(1) here too?

The rest of the patch looks good.

Daniel Jordan July 13, 2018, 6:55 p.m. UTC | #2

On Fri, Jul 13, 2018 at 11:38:19AM -0700, Daniel Jordan wrote:
> On Fri, Jul 13, 2018 at 07:36:32AM +0800, Huang, Ying wrote:
> > @@ -1260,7 +1257,6 @@ static void swapcache_free(swp_entry_t entry)
> >  	}
> >  }
> >  
> > -#ifdef CONFIG_THP_SWAP
> >  static void swapcache_free_cluster(swp_entry_t entry)
> >  {
> >  	unsigned long offset = swp_offset(entry);
> > @@ -1271,6 +1267,9 @@ static void swapcache_free_cluster(swp_entry_t entry)
> >  	unsigned int i, free_entries = 0;
> >  	unsigned char val;
> >  
> > +	if (!IS_ENABLED(CONFIG_THP_SWAP))
> > +		return;
> > +
> 
> VM_WARN_ON_ONCE(1) here too?

Nevermind, this branch goes away later in the series.

Patch

diff --git a/mm/swapfile.c b/mm/swapfile.c
index e31aa601d9c0..75c84aa763a3 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -870,7 +870,6 @@  static int scan_swap_map_slots(struct swap_info_struct *si,
 	return n_ret;
 }
 
-#ifdef CONFIG_THP_SWAP
 static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
 {
 	unsigned long idx;
@@ -878,6 +877,11 @@  static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
 	unsigned long offset, i;
 	unsigned char *map;
 
+	if (!IS_ENABLED(CONFIG_THP_SWAP)) {
+		VM_WARN_ON_ONCE(1);
+		return 0;
+	}
+
 	if (cluster_list_empty(&si->free_clusters))
 		return 0;
 
@@ -908,13 +912,6 @@  static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
 	unlock_cluster(ci);
 	swap_range_free(si, offset, SWAPFILE_CLUSTER);
 }
-#else
-static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
-{
-	VM_WARN_ON_ONCE(1);
-	return 0;
-}
-#endif /* CONFIG_THP_SWAP */
 
 static unsigned long scan_swap_map(struct swap_info_struct *si,
 				   unsigned char usage)
@@ -1260,7 +1257,6 @@  static void swapcache_free(swp_entry_t entry)
 	}
 }
 
-#ifdef CONFIG_THP_SWAP
 static void swapcache_free_cluster(swp_entry_t entry)
 {
 	unsigned long offset = swp_offset(entry);
@@ -1271,6 +1267,9 @@  static void swapcache_free_cluster(swp_entry_t entry)
 	unsigned int i, free_entries = 0;
 	unsigned char val;
 
+	if (!IS_ENABLED(CONFIG_THP_SWAP))
+		return;
+
 	si = _swap_info_get(entry);
 	if (!si)
 		return;
@@ -1306,6 +1305,7 @@  static void swapcache_free_cluster(swp_entry_t entry)
 	}
 }
 
+#ifdef CONFIG_THP_SWAP
 int split_swap_cluster(swp_entry_t entry)
 {
 	struct swap_info_struct *si;
@@ -1320,11 +1320,7 @@  int split_swap_cluster(swp_entry_t entry)
 	unlock_cluster(ci);
 	return 0;
 }
-#else
-static inline void swapcache_free_cluster(swp_entry_t entry)
-{
-}
-#endif /* CONFIG_THP_SWAP */
+#endif
 
 void put_swap_page(struct page *page, swp_entry_t entry)
 {
@@ -1483,7 +1479,6 @@  int swp_swapcount(swp_entry_t entry)
 	return count;
 }
 
-#ifdef CONFIG_THP_SWAP
 static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
 					 swp_entry_t entry)
 {
@@ -1494,6 +1489,9 @@  static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
 	int i;
 	bool ret = false;
 
+	if (!IS_ENABLED(CONFIG_THP_SWAP))
+		return swap_swapcount(si, entry) != 0;
+
 	ci = lock_cluster_or_swap_info(si, offset);
 	if (!ci || !cluster_is_huge(ci)) {
 		if (map[roffset] != SWAP_HAS_CACHE)
@@ -1516,7 +1514,7 @@  static bool page_swapped(struct page *page)
 	swp_entry_t entry;
 	struct swap_info_struct *si;
 
-	if (likely(!PageTransCompound(page)))
+	if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page)))
 		return page_swapcount(page) != 0;
 
 	page = compound_head(page);
@@ -1540,10 +1538,8 @@  static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
 	/* hugetlbfs shouldn't call it */
 	VM_BUG_ON_PAGE(PageHuge(page), page);
 
-	if (likely(!PageTransCompound(page))) {
-		mapcount = atomic_read(&page->_mapcount) + 1;
-		if (total_mapcount)
-			*total_mapcount = mapcount;
+	if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
+		mapcount = page_trans_huge_mapcount(page, total_mapcount);
 		if (PageSwapCache(page))
 			swapcount = page_swapcount(page);
 		if (total_swapcount)
@@ -1590,26 +1586,6 @@  static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
 
 	return map_swapcount;
 }
-#else
-#define swap_page_trans_huge_swapped(si, entry)	swap_swapcount(si, entry)
-#define page_swapped(page)			(page_swapcount(page) != 0)
-
-static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
-					 int *total_swapcount)
-{
-	int mapcount, swapcount = 0;
-
-	/* hugetlbfs shouldn't call it */
-	VM_BUG_ON_PAGE(PageHuge(page), page);
-
-	mapcount = page_trans_huge_mapcount(page, total_mapcount);
-	if (PageSwapCache(page))
-		swapcount = page_swapcount(page);
-	if (total_swapcount)
-		*total_swapcount = swapcount;
-	return mapcount + swapcount;
-}
-#endif
 
 /*
  * We can write to an anon page without COW if there are no other references