zswap: use PAGE_SIZE * 2 for compression dst buffer size when calling crypto compression API

["Um, Taeil" <taeilum@amazon.com>]

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Currently, we allocate PAGE_SIZE * 2 for zswap_dstmem which is used as compression destination buffer.
However, we pass only half of the size (PAGE_SIZE) to crypto_comp_compress.
This might not be a problem for CPU based existing lzo, lz4 crypto compression driver implantation.
However, this could be a problem for some H/W acceleration compression drivers, which honor destination buffer size when it prepares H/W resources.
Actually, this patch is aligned with what zram is passing when it calls crypto_comp_compress.
The following simple patch will solve this problem. I tested it with existing crypto/lzo.c and crypto/lz4.c compression driver and it works fine.


--- mm/zswap.c.orig       2018-09-14 14:36:37.984199232 -0700
+++ mm/zswap.c             2018-09-14 14:36:53.340189681 -0700
@@ -1001,7 +1001,7 @@ static int zswap_frontswap_store(unsigne
                struct zswap_entry *entry, *dupentry;
                struct crypto_comp *tfm;
                int ret;
-              unsigned int hlen, dlen = PAGE_SIZE;
+             unsigned int hlen, dlen = PAGE_SIZE * 2;
                unsigned long handle, value;
                char *buf;
                u8 *src, *dst;



Thank you,
Taeil


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