linux-kernel - [PATCH 3/4] zswap: Zero-filled pages handling

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Message-id: <1267599031.7838.1471585908108.JavaMail.weblogic@epwas3p2>
Date:   Fri, 19 Aug 2016 05:51:48 +0000
From:   Srividya Desireddy <srividya.dr@...sung.com>
To:     penberg@...nel.org
Cc:     Srividya Desireddy <srividya.dr@...sung.com>,
        sjenning@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Dinakar Reddy Pathireddy 
        <dinakar.p@...sung.com>,
        샤란 <sharan.allur@...sung.com>,
        SUNEEL KUMAR SURIMANI <suneel@...sung.com>,
        김주훈 <juhunkim@...sung.com>
Subject:  [PATCH 3/4] zswap: Zero-filled pages handling

On 17 August 2016 at 17:55, Pekka Enberg <penberg@...nel.org> wrote:
> On Wed, Aug 17, 2016 at 1:18 PM, Srividya Desireddy
> <srividya.dr@...sung.com> wrote:
>> @@ -1314,6 +1347,13 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>         }
>>         spin_unlock(&tree->lock);
>>
>> +       if (entry->zeroflag) {
>> +               dst = kmap_atomic(page);
>> +               memset(dst, 0, PAGE_SIZE);
>> +               kunmap_atomic(dst);
>> +               goto freeentry;
>> +       }
>
> Don't we need the same thing in zswap_writeback_entry() for the
> ZSWAP_SWAPCACHE_NEW case?

Zero-filled pages are not compressed and stored in the zpool memory.
Zpool handle will not be created for zero-filled pages, hence they
can not be picked for eviction/writeback to the swap device.

- Srividya
>
>> +
>>         /* decompress */
>>         dlen = PAGE_SIZE;
>>         src = (u8 *)zpool_map_handle(entry->pool->zpool, entry->zhandle->handle,
>> @@ -1327,6 +1367,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>>         zpool_unmap_handle(entry->pool->zpool, entry->zhandle->handle);
>>         BUG_ON(ret);
>
> - Pekka