[PATCH] zswap: do not allocate from atomic pool

[Sergey Senozhatsky]

zswap_frontswap_load() should be called from preemptible
context (we even call mutex_lock() there) and it does not
look like we need to do GFP_ATOMIC allocaion for temp
buffer. The same applies to zswap_writeback_entry().

Use GFP_KERNEL for temporary buffer allocation in both
cases.

Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 mm/zpool.c | 7 +++++++
 mm/zswap.c | 4 ++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/zpool.c b/mm/zpool.c
index 68facc193496..f46c0d5e766c 100644
--- a/mm/zpool.c
+++ b/mm/zpool.c
@@ -387,6 +387,13 @@ bool zpool_evictable(struct zpool *zpool)
  * zpool_can_sleep_mapped - Test if zpool can sleep when do mapped.
  * @zpool:	The zpool to test
  *
+ * Some allocators enter non-preemptible context in ->map() callback (e.g.
+ * disable pagefaults) and exit that context in ->unmap(), which limits what
+ * we can do with the mapped object. For instance, we cannot wait for
+ * asynchronous crypto API to decompress such an object or take mutexes
+ * since those will call into the scheduler. This function tells us whether
+ * we use such an allocator.
+ *
  * Returns: true if zpool can sleep; false otherwise.
  */
 bool zpool_can_sleep_mapped(struct zpool *zpool)
diff --git a/mm/zswap.c b/mm/zswap.c
index 2d48fd59cc7a..3019f0bde194 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -958,7 +958,7 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 	};
 
 	if (!zpool_can_sleep_mapped(pool)) {
-		tmp = kmalloc(PAGE_SIZE, GFP_ATOMIC);
+		tmp = kmalloc(PAGE_SIZE, GFP_KERNEL);
 		if (!tmp)
 			return -ENOMEM;
 	}
@@ -1311,7 +1311,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 	}
 
 	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
-		tmp = kmalloc(entry->length, GFP_ATOMIC);
+		tmp = kmalloc(entry->length, GFP_KERNEL);
 		if (!tmp) {
 			ret = -ENOMEM;
 			goto freeentry;
-- 
2.38.1.584.g0f3c55d4c2-goog