[PATCH v5 15/18] zram: permit reclaim in zstd custom allocator

[Sergey Senozhatsky]

When configured with pre-trained compression/decompression
dictionary support, zstd requires custom memory allocator,
which it calls internally from compression()/decompression()
routines.  That means allocation from atomic context (either
under entry spin-lock, or per-CPU local-lock or both).  Now,
with non-atomic zram read()/write(), those limitations are
relaxed and we can allow direct and indirect reclaim.

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 drivers/block/zram/backend_zstd.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/block/zram/backend_zstd.c b/drivers/block/zram/backend_zstd.c
index 1184c0036f44..53431251ea62 100644
--- a/drivers/block/zram/backend_zstd.c
+++ b/drivers/block/zram/backend_zstd.c
@@ -24,19 +24,14 @@ struct zstd_params {
 /*
  * For C/D dictionaries we need to provide zstd with zstd_custom_mem,
  * which zstd uses internally to allocate/free memory when needed.
- *
- * This means that allocator.customAlloc() can be called from zcomp_compress()
- * under local-lock (per-CPU compression stream), in which case we must use
- * GFP_ATOMIC.
- *
- * Another complication here is that we can be configured as a swap device.
  */
 static void *zstd_custom_alloc(void *opaque, size_t size)
 {
-	if (!preemptible())
+	/* Technically this should not happen */
+	if (WARN_ON_ONCE(!preemptible()))
 		return kvzalloc(size, GFP_ATOMIC);
 
-	return kvzalloc(size, __GFP_KSWAPD_RECLAIM | __GFP_NOWARN);
+	return kvzalloc(size, GFP_NOIO | __GFP_NOWARN);
 }
 
 static void zstd_custom_free(void *opaque, void *address)
-- 
2.48.1.502.g6dc24dfdaf-goog