[v3,7/9] mm/swapfile: remove stale reuse_swap_page()

Commit Message

David Hildenbrand Jan. 31, 2022, 4:29 p.m. UTC

All users are gone, let's remove it. We'll let SWP_STABLE_WRITES stick
around for now, as it might come in handy in the near future.

Signed-off-by: David Hildenbrand <[e-mail]>
---
 include/linux/swap.h |   4 --
 mm/swapfile.c        | 104 -------------------------------------------
 2 files changed, 108 deletions(-)

Comments

Christoph Hellwig Feb. 2, 2022, 2:35 p.m. UTC | #1

On Mon, Jan 31, 2022 at 05:29:37PM +0100, David Hildenbrand wrote:
> All users are gone, let's remove it. We'll let SWP_STABLE_WRITES stick
> around for now, as it might come in handy in the near future.

I don't think leaving a flag that has no user an a completely trivial
place to set it around is a good idea.  This is a classic case of
bitrot.

David Hildenbrand Feb. 2, 2022, 5:01 p.m. UTC | #2

On 02.02.22 15:35, Christoph Hellwig wrote:
> On Mon, Jan 31, 2022 at 05:29:37PM +0100, David Hildenbrand wrote:
>> All users are gone, let's remove it. We'll let SWP_STABLE_WRITES stick
>> around for now, as it might come in handy in the near future.
> 
> I don't think leaving a flag that has no user an a completely trivial
> place to set it around is a good idea.  This is a classic case of
> bitrot.

Right now I'm planning on using it in part 2 -- on which I'm currently
working on. If I don't end up reusing it, I'll remember to remove it.

Vlastimil Babka March 10, 2022, 10:44 a.m. UTC | #3

On 1/31/22 17:29, David Hildenbrand wrote:
> All users are gone, let's remove it. We'll let SWP_STABLE_WRITES stick
> around for now, as it might come in handy in the near future.
> 
> Signed-off-by: David Hildenbrand <[e-mail]>

Nice cleanup.

Acked-by: Vlastimil Babka <[e-mail]>

Patch

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1d38d9475c4d..b546e4bd5c5a 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -514,7 +514,6 @@  extern int __swp_swapcount(swp_entry_t entry);
 extern int swp_swapcount(swp_entry_t entry);
 extern struct swap_info_struct *page_swap_info(struct page *);
 extern struct swap_info_struct *swp_swap_info(swp_entry_t entry);
-extern bool reuse_swap_page(struct page *);
 extern int try_to_free_swap(struct page *);
 struct backing_dev_info;
 extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
@@ -680,9 +679,6 @@  static inline int swp_swapcount(swp_entry_t entry)
 	return 0;
 }
 
-#define reuse_swap_page(page) \
-	(page_trans_huge_mapcount(page) == 1)
-
 static inline int try_to_free_swap(struct page *page)
 {
 	return 0;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index bf0df7aa7158..a5183315dc58 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1167,16 +1167,6 @@  static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
 	return NULL;
 }
 
-static struct swap_info_struct *swap_info_get(swp_entry_t entry)
-{
-	struct swap_info_struct *p;
-
-	p = _swap_info_get(entry);
-	if (p)
-		spin_lock(&p->lock);
-	return p;
-}
-
 static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry,
 					struct swap_info_struct *q)
 {
@@ -1601,100 +1591,6 @@  static bool page_swapped(struct page *page)
 	return false;
 }
 
-static int page_trans_huge_map_swapcount(struct page *page,
-					 int *total_swapcount)
-{
-	int i, map_swapcount, _total_swapcount;
-	unsigned long offset = 0;
-	struct swap_info_struct *si;
-	struct swap_cluster_info *ci = NULL;
-	unsigned char *map = NULL;
-	int swapcount = 0;
-
-	/* hugetlbfs shouldn't call it */
-	VM_BUG_ON_PAGE(PageHuge(page), page);
-
-	if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!PageTransCompound(page))) {
-		if (PageSwapCache(page))
-			swapcount = page_swapcount(page);
-		if (total_swapcount)
-			*total_swapcount = swapcount;
-		return swapcount + page_trans_huge_mapcount(page);
-	}
-
-	page = compound_head(page);
-
-	_total_swapcount = map_swapcount = 0;
-	if (PageSwapCache(page)) {
-		swp_entry_t entry;
-
-		entry.val = page_private(page);
-		si = _swap_info_get(entry);
-		if (si) {
-			map = si->swap_map;
-			offset = swp_offset(entry);
-		}
-	}
-	if (map)
-		ci = lock_cluster(si, offset);
-	for (i = 0; i < HPAGE_PMD_NR; i++) {
-		int mapcount = atomic_read(&page[i]._mapcount) + 1;
-		if (map) {
-			swapcount = swap_count(map[offset + i]);
-			_total_swapcount += swapcount;
-		}
-		map_swapcount = max(map_swapcount, mapcount + swapcount);
-	}
-	unlock_cluster(ci);
-
-	if (PageDoubleMap(page))
-		map_swapcount -= 1;
-
-	if (total_swapcount)
-		*total_swapcount = _total_swapcount;
-
-	return map_swapcount + compound_mapcount(page);
-}
-
-/*
- * We can write to an anon page without COW if there are no other references
- * to it.  And as a side-effect, free up its swap: because the old content
- * on disk will never be read, and seeking back there to write new content
- * later would only waste time away from clustering.
- */
-bool reuse_swap_page(struct page *page)
-{
-	int count, total_swapcount;
-
-	VM_BUG_ON_PAGE(!PageLocked(page), page);
-	if (unlikely(PageKsm(page)))
-		return false;
-	count = page_trans_huge_map_swapcount(page, &total_swapcount);
-	if (count == 1 && PageSwapCache(page) &&
-	    (likely(!PageTransCompound(page)) ||
-	     /* The remaining swap count will be freed soon */
-	     total_swapcount == page_swapcount(page))) {
-		if (!PageWriteback(page)) {
-			page = compound_head(page);
-			delete_from_swap_cache(page);
-			SetPageDirty(page);
-		} else {
-			swp_entry_t entry;
-			struct swap_info_struct *p;
-
-			entry.val = page_private(page);
-			p = swap_info_get(entry);
-			if (p->flags & SWP_STABLE_WRITES) {
-				spin_unlock(&p->lock);
-				return false;
-			}
-			spin_unlock(&p->lock);
-		}
-	}
-
-	return count <= 1;
-}
-
 /*
  * If swap is getting full, or if there are no more mappings of this page,
  * then try_to_free_swap is called to free its swap space.