Increasing MAXPHYS

Matthew Dillon dillon at
Sat Mar 20 18:22:11 UTC 2010

:Pardon my ignorance, but wouldn't so much KVM make small embedded
:devices like Soekris boards with 128 MB of physical RAM totally unusable
:then? On my net4801, running RELENG_8:
:vm.kmem_size: 40878080
:hw.physmem: 125272064
:hw.usermen: 84840448
:hw.realmem: 134217728

    KVM != physical memory.  On i386 by default the kernel has 1G of KVM
    and userland has 3G.  While the partition can be moved to increase
    available KVM on i386 (e.g. 2G/2G), it isn't recommended.

    So the KVM reserved for various things does not generally impact
    physical memory use.

    The number of swap buffers (nswbuf) is scaled to 1/4 nbufs with a
    maximum of 256.  Systems with small amounts of memory should not be

    The issue w/ regards to KVM problems on i386 is mostly restricted to
    systems with 2G+ of ram where the kernel's various internal parameters
    are scaled to their maximum values or limits.  On systems with less ram
    the kernel's internal parameters are usually scaled down sufficiently
    that there is very little chance of the kernel running out of KVM.


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