zram: permit reclaim in zstd custom allocator

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.

Link: https://lkml.kernel.org/r/20250221222958.2225035-15-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/block/zram/backend_zstd.c b/drivers/block/zram/backend_zstd.c
index 1184c0036f44bde18cb39885865c93a1fec47301..53431251ea6232198da4aad919d2d661b8be4333 100644 (file)
--- 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)