From: Dan Streetman <ddstreet@ieee.org>
To: Timofey Titovets <nefelim4ag@gmail.com>
Cc: Srividya Desireddy <srividya.dr@samsung.com>,
"sjenning@redhat.com" <sjenning@redhat.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>
Subject: Re: [PATCH] zswap: Same-filled pages handling
Date: Fri, 17 Nov 2017 17:07:19 -0500 [thread overview]
Message-ID: <CALZtONASdY1rHyN6s=YyV4uKg6QtZk=tnRV=bRnvq4d1JAUVyQ@mail.gmail.com> (raw)
In-Reply-To: <CAGqmi75Y9wbwBS0ZythcNF1gi6bW7g_XcuMDgLu=Nx4=pWC8Jw@mail.gmail.com>
On Wed, Oct 18, 2017 at 5:31 PM, Timofey Titovets <nefelim4ag@gmail.com> wrote:
>> +static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
>> +{
>> + unsigned int pos;
>> + unsigned long *page;
>> +
>> + page = (unsigned long *)ptr;
>> + for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) {
>> + if (page[pos] != page[0])
>> + return 0;
>> + }
>> + *value = page[0];
>> + return 1;
>> +}
>> +
>
> In theory you can speedup that check by memcmp(),
> And do something like first:
> memcmp(ptr, ptr + PAGE_SIZE/sizeof(*page)/2, PAGE_SIZE/2);
> After compare 1/4 with 2/4
> Then 1/8 with 2/8.
> And after do you check with pattern, only on first 512 bytes.
>
> Just because memcmp() on fresh CPU are crazy fast.
> That can easy make you check less expensive.
I did check this, and it is actually significantly worse; keep in mind
that doing it ^ way may is a smaller loop, but is actually doing more
memory comparisons.
>
>> +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().
>
> P.S.
> I'm just too busy to make fast performance test in user space,
> but my recent experience with that CPU commands, show what that make a sense:
> KSM patch: https://patchwork.kernel.org/patch/9980803/
> User space tests: https://github.com/Nefelim4ag/memcmpe
> PAGE_SIZE: 65536, loop count: 1966080
> memcmp: -28 time: 3216 ms, th: 40064.644611 MiB/s
> memcmpe: -28, offset: 62232 time: 3588 ms, th: 35902.462390 MiB/s
> memcmpe: -28, offset: 62232 time: 71 ms, th: 1792233.164286 MiB/s
>
> IIRC, with code like our, you must see ~2.5GiB/s
>
> Thanks.
> --
> Have a nice day,
> Timofey.
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next prev parent reply other threads:[~2017-11-17 22:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1>
2017-10-18 10:48 ` [PATCH] zswap: Same-filled pages handling Srividya Desireddy
2017-10-18 12:34 ` Matthew Wilcox
2017-10-18 13:33 ` Timofey Titovets
2017-10-18 14:11 ` Matthew Wilcox
2017-10-18 20:43 ` Andi Kleen
2017-10-19 1:10 ` Matthew Wilcox
2017-10-19 4:30 ` Andi Kleen
2017-10-19 13:24 ` Matthew Wilcox
2017-10-18 21:31 ` Timofey Titovets
2017-10-19 1:08 ` Matthew Wilcox
[not found] ` <CGME20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p3>
2017-11-02 15:08 ` Srividya Desireddy
2017-11-17 22:10 ` Dan Streetman
2017-11-17 22:07 ` Dan Streetman [this message]
2017-11-17 21:27 ` Dan Streetman
2017-11-20 23:46 ` Andrew Morton
2017-11-28 11:35 ` Dan Streetman
[not found] ` <CGME20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p6>
2017-11-29 15:34 ` [PATCH] zswap: Update with same-value filled page feature Srividya Desireddy
2017-11-29 21:29 ` Dan Streetman
2017-12-06 11:48 ` [PATCH v2] " Srividya Desireddy
2017-12-06 15:20 ` Dan Streetman
[not found] ` <CGME20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p4>
2017-11-21 14:18 ` [PATCH v2] zswap: Same-filled pages handling Srividya Desireddy
2017-10-18 14:43 ` [PATCH] " Srividya Desireddy
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