Date: Tue, 3 Jan 2012 09:34:54 +0100 From: Marc Olzheim <marcolz@stack.nl> To: Garrett Cooper <yanegomi@gmail.com> Cc: freebsd-performance@freebsd.org, Dieter BSD <dieterbsd@engineer.com> Subject: Re: cmp(1) has a bottleneck, but where? Message-ID: <20120103083454.GA22673@zlo.nu> In-Reply-To: <CAGH67wQXuMasyc9BE8M9fHsQv6d2zdRxDQ2ekX4whjHJFyqZyg@mail.gmail.com> References: <20120103073736.218240@gmx.com> <CAGH67wQXuMasyc9BE8M9fHsQv6d2zdRxDQ2ekX4whjHJFyqZyg@mail.gmail.com>
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On Tue, Jan 03, 2012 at 12:21:10AM -0800, Garrett Cooper wrote:
> The file is 3.0GB in size. Look at all those page faults though!
> Thanks!
> -Garrett
From usr.bin/cmp/c_regular.c:
#define MMAP_CHUNK (8*1024*1024)
...
for (..) {
mmap() chunk of size MMAP_CHUNK.
compare
munmap()k
}
That 8 MB chunk size sounds like a bad plan to me. I can imagine
something needed to be done to compare files larger than X GB on a 32bit
system, but 8MB is pretty small...
Marc
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