Date: Fri, 06 Sep 2013 12:14:27 -0700 From: Alfred Perlstein <bright@mu.org> To: hiren panchasara <hiren.panchasara@gmail.com> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: mbuf autotuning changes Message-ID: <522A2993.6020206@mu.org> In-Reply-To: <CALCpEUFxaXKh4%2B8evratZYE3JyfyTmrL7rzpBqUJ%2B_S3Ff-AcA@mail.gmail.com> References: <CALCpEUFxaXKh4%2B8evratZYE3JyfyTmrL7rzpBqUJ%2B_S3Ff-AcA@mail.gmail.com>
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On 9/6/13 12:10 PM, hiren panchasara wrote:
> tunable_mbinit() in kern_mbuf.c looks like this:
>
> 119 /*
> 120 * The default limit for all mbuf related memory is 1/2 of all
> 121 * available kernel memory (physical or kmem).
> 122 * At most it can be 3/4 of available kernel memory.
> 123 */
> 124 realmem = qmin((quad_t)physmem * PAGE_SIZE,
> 125 vm_map_max(kmem_map) - vm_map_min(kmem_map));
> 126 maxmbufmem = realmem / 2;
> 127 TUNABLE_QUAD_FETCH("kern.ipc.maxmbufmem", &maxmbufmem);
> 128 if (maxmbufmem > realmem / 4 * 3)
> 129 maxmbufmem = realmem / 4 * 3;
>
> If I am reading the code correctly, we loose the value on line 126 when we
> do FETCH on line 127.
>
> And after line 127, if we havent specified kern.ipc.maxmbufmem (in
> loader.conf - I guess...), we set that value to 0.
>
> And because of that the if condition on line 128 is almost always false?
>
> What am I missing here?
>
> Thanks,
> Hiren
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I think TUNABLE_*_FETCH will only write to the variable if it explicitly
set.
Meaning, unless the user actually sets a value in loader.conf then 127
is a no-op.
-Alfred
--
Alfred Perlstein
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