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

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Date:   Sat, 22 May 2021 17:22:41 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>, <sjenning@...hat.com>,
        <ddstreet@...e.org>, <vitaly.wool@...sulko.com>
CC:     <bigeasy@...utronix.de>, <nathan@...nel.org>,
        <colin.king@...onical.com>, <tiantao6@...ilicon.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH 2/3] 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.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.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