linux-kernel - Re: [PATCH] zswap: Same-filled pages handling

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Message-ID: <CAGqmi77nDU+z2PhNFJq3i208mxMbdTdk2=uPwfj42y0G3yyiWw@mail.gmail.com>
Date:   Wed, 18 Oct 2017 16:33:43 +0300
From:   Timofey Titovets <nefelim4ag@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Srividya Desireddy <srividya.dr@...sung.com>,
        "sjenning@...hat.com" <sjenning@...hat.com>,
        "ddstreet@...e.org" <ddstreet@...e.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "penberg@...nel.org" <penberg@...nel.org>,
        Dinakar Reddy Pathireddy <dinakar.p@...sung.com>,
        SHARAN ALLUR <sharan.allur@...sung.com>,
        RAJIB BASU <rajib.basu@...sung.com>,
        JUHUN KIM <juhunkim@...sung.com>,
        "srividya.desireddy@...il.com" <srividya.desireddy@...il.com>
Subject: Re: [PATCH] zswap: Same-filled pages handling

2017-10-18 15:34 GMT+03:00 Matthew Wilcox <willy@...radead.org>:
> On Wed, Oct 18, 2017 at 10:48:32AM +0000, Srividya Desireddy 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;
>> +     }
>> +}
>
> I think you meant:
>
> static void zswap_fill_page(void *ptr, unsigned long value)
> {
>         memset_l(ptr, value, PAGE_SIZE / sizeof(unsigned long));
> }
>
> (and you should see significantly better numbers at least on x86;
> I don't know if anyone's done an arm64 version of memset_l yet).
>
> --
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IIRC kernel have special zero page, and if i understand correctly.
You can map all zero pages to that zero page and not touch zswap completely.
(Your situation look like some KSM case (i.e. KSM can handle pages
with same content), but i'm not sure if that applicable there)

Thanks.
-- 
Have a nice day,
Timofey.