[patch 106/192] mm/zswap.c: avoid unnecessary copy-in at map time

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From: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Subject: mm/zswap.c: avoid unnecessary copy-in at map time

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.

Link: https://lkml.kernel.org/r/20210522092242.3233191-3-linmiaohe@xxxxxxxxxx
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Dan Streetman <ddstreet@xxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxx>
Cc: Tian Tao <tiantao6@xxxxxxxxxxxxx>
Cc: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/zswap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/zswap.c~mm-zswapc-avoid-unnecessary-copy-in-at-map-time
+++ a/mm/zswap.c
@@ -1203,7 +1203,7 @@ static int zswap_frontswap_store(unsigne
 		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);
_



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