[PATCH 0/3] Cleanup and fixup for zswap

[PATCH 0/3] Cleanup and fixup for zswap

[Miaohe Lin]

Hi all,
This series contains cleanups to remove unused function and avoid
unnecessary copy-in at map time. Also this fixes two bugs in the
function zswap_writeback_entry(). More details can be found in the
respective changelogs. Thanks!

Miaohe Lin (3):
  mm/zswap.c: remove unused function zswap_debugfs_exit()
  mm/zswap.c: avoid unnecessary copy-in at map time
  mm/zswap.c: fix two bugs in zswap_writeback_entry()

 mm/zswap.c | 26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

-- 
2.23.0

[PATCH 1/3] mm/zswap.c: remove unused function zswap_debugfs_exit()

[Miaohe Lin]

zswap_debugfs_exit() is unused, remove it.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/zswap.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 20763267a219..e93459319fdb 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1427,18 +1427,11 @@ static int __init zswap_debugfs_init(void)
 
 	return 0;
 }
-
-static void __exit zswap_debugfs_exit(void)
-{
-	debugfs_remove_recursive(zswap_debugfs_root);
-}
 #else
 static int __init zswap_debugfs_init(void)
 {
 	return 0;
 }
-
-static void __exit zswap_debugfs_exit(void) { }
 #endif
 
 /*********************************
-- 
2.23.0

[PATCH 2/3] mm/zswap.c: avoid unnecessary copy-in at map time

[Miaohe Lin]

The buf mapped via zpool_map_handle() is only used to store compressed
page buffer and there is no information to extract from it. So we could
use ZPOOL_MM_WO instead to avoid unnecessary copy-in at map time.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/zswap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index e93459319fdb..c27ce9f2cdf8 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1203,7 +1203,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 		zswap_reject_alloc_fail++;
 		goto put_dstmem;
 	}
-	buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_RW);
+	buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_WO);
 	memcpy(buf, &zhdr, hlen);
 	memcpy(buf + hlen, dst, dlen);
 	zpool_unmap_handle(entry->pool->zpool, handle);
-- 
2.23.0

[PATCH 3/3] mm/zswap.c: fix two bugs in zswap_writeback_entry()

[Miaohe Lin]

In the ZSWAP_SWAPCACHE_FAIL and ZSWAP_SWAPCACHE_EXIST case, we forgot to
call zpool_unmap_handle() when zpool can't sleep. And we might sleep in
zswap_get_swap_cache_page() while zpool can't sleep. To fix all of these,
zpool_unmap_handle() should be done before zswap_get_swap_cache_page()
when zpool can't sleep.

Fixes: fc6697a89f56 ("mm/zswap: add the flag can_sleep_mapped")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/zswap.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index c27ce9f2cdf8..7944e3e57e78 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -967,6 +967,13 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 	spin_unlock(&tree->lock);
 	BUG_ON(offset != entry->offset);
 
+	src = (u8 *)zhdr + sizeof(struct zswap_header);
+	if (!zpool_can_sleep_mapped(pool)) {
+		memcpy(tmp, src, entry->length);
+		src = tmp;
+		zpool_unmap_handle(pool, handle);
+	}
+
 	/* try to allocate swap cache page */
 	switch (zswap_get_swap_cache_page(swpentry, &page)) {
 	case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
@@ -982,17 +989,7 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 	case ZSWAP_SWAPCACHE_NEW: /* page is locked */
 		/* decompress */
 		acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
-
 		dlen = PAGE_SIZE;
-		src = (u8 *)zhdr + sizeof(struct zswap_header);
-
-		if (!zpool_can_sleep_mapped(pool)) {
-
-			memcpy(tmp, src, entry->length);
-			src = tmp;
-
-			zpool_unmap_handle(pool, handle);
-		}
 
 		mutex_lock(acomp_ctx->mutex);
 		sg_init_one(&input, src, entry->length);
-- 
2.23.0