[PATCH] z3fold: discourage use of pages that weren't compacted

[Vitaly Wool]

If a z3fold page couldn't be compacted, we don't want it to be
used for next object allocation in the first place. It makes more
sense to add it to the end of the relevant unbuddied list. If that
page gets compacted later, it will be added to the beginning of
the list then.

This simple idea gives 5-7% improvement in randrw fio tests and
about 10% improvement in fio sequential read/write.

Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx>
---
 mm/z3fold.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 5fe2652..eb8f9a0 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -277,10 +277,10 @@ static inline void *mchunk_memmove(struct z3fold_header *zhdr,
 
 #define BIG_CHUNK_GAP	3
 /* Has to be called with lock held */
-static int z3fold_compact_page(struct z3fold_header *zhdr)
+static bool z3fold_compact_page(struct z3fold_header *zhdr)
 {
 	struct page *page = virt_to_page(zhdr);
-	int ret = 0;
+	bool ret = false;
 
 	if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
 		goto out;
@@ -292,7 +292,7 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
 			zhdr->middle_chunks = 0;
 			zhdr->start_middle = 0;
 			zhdr->first_num++;
-			ret = 1;
+			ret = true;
 			goto out;
 		}
 
@@ -304,7 +304,7 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
 		    zhdr->start_middle > zhdr->first_chunks + BIG_CHUNK_GAP) {
 			mchunk_memmove(zhdr, zhdr->first_chunks + 1);
 			zhdr->start_middle = zhdr->first_chunks + 1;
-			ret = 1;
+			ret = true;
 			goto out;
 		}
 		if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
@@ -314,7 +314,7 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
 				zhdr->middle_chunks;
 			mchunk_memmove(zhdr, new_start);
 			zhdr->start_middle = new_start;
-			ret = 1;
+			ret = true;
 			goto out;
 		}
 	}
@@ -535,11 +535,19 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 		free_z3fold_page(zhdr);
 		atomic64_dec(&pool->pages_nr);
 	} else {
-		z3fold_compact_page(zhdr);
+		bool compacted = z3fold_compact_page(zhdr);
 		/* Add to the unbuddied list */
 		spin_lock(&pool->lock);
 		freechunks = num_free_chunks(zhdr);
-		list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+		/*
+		 * If the page has been compacted, we want to use it
+		 * in the first place.
+		 */
+		if (compacted)
+			list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
+		else
+			list_add_tail(&zhdr->buddy,
+				      &pool->unbuddied[freechunks]);
 		spin_unlock(&pool->lock);
 		z3fold_page_unlock(zhdr);
 	}
@@ -668,12 +676,16 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 				spin_lock(&pool->lock);
 				list_add(&zhdr->buddy, &pool->buddied);
 			} else {
-				z3fold_compact_page(zhdr);
+				bool compacted = z3fold_compact_page(zhdr);
 				/* add to unbuddied list */
 				spin_lock(&pool->lock);
 				freechunks = num_free_chunks(zhdr);
-				list_add(&zhdr->buddy,
-					 &pool->unbuddied[freechunks]);
+				if (compacted)
+					list_add(&zhdr->buddy,
+						&pool->unbuddied[freechunks]);
+				else
+					list_add_tail(&zhdr->buddy,
+						&pool->unbuddied[freechunks]);
 			}
 		}
 
-- 
2.4.2