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From: Dan Streetman <ddstreet@ieee.org>
Date: Fri, 17 Nov 2017 17:10:33 -0500
Message-ID: <CALZtONBh5vmfnC4G1d66AQtmBB8DJA8c3yZWZYg01maKCjVagA@mail.gmail.com>
Subject: Re: [PATCH] zswap: Same-filled pages handling
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To: srividya.dr@samsung.com
Cc: "sjenning@redhat.com" <sjenning@redhat.com>, Matthew Wilcox <willy@infradead.org>, Timofey Titovets <nefelim4ag@gmail.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "penberg@kernel.org" <penberg@kernel.org>, Dinakar Reddy Pathireddy <dinakar.p@samsung.com>, SHARAN ALLUR <sharan.allur@samsung.com>, RAJIB BASU <rajib.basu@samsung.com>, JUHUN KIM <juhunkim@samsung.com>, "srividya.desireddy@gmail.com" <srividya.desireddy@gmail.com>

On Thu, Nov 2, 2017 at 11:08 AM, Srividya Desireddy
<srividya.dr@samsung.com> wrote:
>
> On Wed, Oct 19, 2017 at 6:38 AM, Matthew Wilcox wrote:
>> On Thu, Oct 19, 2017 at 12:31:18AM +0300, Timofey Titovets wrote:
>>> > +static void zswap_fill_page(void *ptr, unsigned long value)
>>> > +{
>>> > +       unsigned int pos;
>>> > +       unsigned long *page;
>>> > +
>>> > +       page = (unsigned long *)ptr;
>>> > +       if (value == 0)
>>> > +               memset(page, 0, PAGE_SIZE);
>>> > +       else {
>>> > +               for (pos = 0; pos < PAGE_SIZE / sizeof(*page); pos++)
>>> > +                       page[pos] = value;
>>> > +       }
>>> > +}
>>>
>>> Same here, but with memcpy().
>>
>>No.  Use memset_l which is optimised for this specific job.
>
> I have tested this patch using memset_l() function in zswap_fill_page() on
> x86 64-bit system with 2GB RAM. The performance remains same.
> But, memset_l() funcion might be optimised in future.
> @Seth Jennings/Dan Streetman:  Should I use memset_l() function in this patch.

my testing showed also showed minimal if any difference when using
memset_l(), but it's simpler code and should never be slower than
looping.  I'll ack it if you want to send an additional patch making
this change (on top of the one I already acked).

>
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