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

[Dan Streetman <ddstreet@ieee.org>]

On Mon, Sep 17, 2018 at 7:10 PM Um, Taeil <taeilum@amazon.com> wrote:
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> Currently, we allocate PAGE_SIZE * 2 for zswap_dstmem which is used as compression destination buffer.
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> However, we pass only half of the size (PAGE_SIZE) to crypto_comp_compress.
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> This might not be a problem for CPU based existing lzo, lz4 crypto compression driver implantation.
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> However, this could be a problem for some H/W acceleration compression drivers, which honor destination buffer size when it prepares H/W resources.

How exactly could it be a problem?

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> Actually, this patch is aligned with what zram is passing when it calls crypto_comp_compress.
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> 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.
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> --- mm/zswap.c.orig       2018-09-14 14:36:37.984199232 -0700
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> +++ mm/zswap.c             2018-09-14 14:36:53.340189681 -0700
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> @@ -1001,7 +1001,7 @@ static int zswap_frontswap_store(unsigne
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>                 struct zswap_entry *entry, *dupentry;
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>                 struct crypto_comp *tfm;
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>                 int ret;
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> -              unsigned int hlen, dlen = PAGE_SIZE;
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> +             unsigned int hlen, dlen = PAGE_SIZE * 2;
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>                 unsigned long handle, value;
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>                 char *buf;
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>                 u8 *src, *dst;
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> Thank you,
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> Taeil
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>