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Date: Fri, 6 Sep 2013 12:10:47 -0700
Message-ID: <CALCpEUFxaXKh4+8evratZYE3JyfyTmrL7rzpBqUJ+_S3Ff-AcA@mail.gmail.com>
Subject: mbuf autotuning changes
From: hiren panchasara <hiren.panchasara@gmail.com>
To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>
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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