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); _
