linux-kernel - Re: [PATCH v2 1/4] introduce zero filled pages handler

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Message-ID: <CAPbh3rvOW2hh0bMTY_FyYJPiyqS4a76pHgDYLGYvLKjEzfJoig@mail.gmail.com>
Date:	Tue, 19 Mar 2013 12:44:22 -0400
From:	Konrad Rzeszutek Wilk <konrad@...nok.org>
To:	Dan Magenheimer <dan.magenheimer@...cle.com>
Cc:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] introduce zero filled pages handler

On Sat, Mar 16, 2013 at 2:24 PM, Dan Magenheimer
<dan.magenheimer@...cle.com> wrote:
>> From: Konrad Rzeszutek Wilk [mailto:konrad@...nok.org]
>> Subject: Re: [PATCH v2 1/4] introduce zero filled pages handler
>>
>> > +
>> > +   for (pos = 0; pos < PAGE_SIZE / sizeof(*page); pos++) {
>> > +           if (page[pos])
>> > +                   return false;
>>
>> Perhaps allocate a static page filled with zeros and just do memcmp?
>
> That seems like a bad idea.  Why compare two different
> memory locations when comparing one memory location
> to a register will do?
>

Good point. I was hoping there was an fast memcmp that would
do fancy SSE registers. But it is memory against memory instead of
registers.

Perhaps a cunning trick would be to check (as a shortcircuit)
check against 'empty_zero_page' and if that check fails, then try
to do the check for each byte in the code?

>
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