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    SubjectRe: workaround large MTU and N-order allocation failures
    On Mon, Sep 19, 2005 at 04:31:02PM +1000, Nick Piggin wrote:
    > On Sun, 2005-09-18 at 17:35 +0300, Dan Aloni wrote:
    > > Hello,
    > >
    > > Is there currently a workaround available for handling large MTU
    > > (larger than 1 page, even 2-order) in the Linux network stack?
    > >
    > > The problem with large MTU is external memory fragmentation in
    > > the buddy system following high workload, causing alloc_skb() to
    > > fail.
    > >
    > > I'm interested in patches for both 2.4 and 2.6 kernels.
    > >
    >
    > Yes there is currently a workaround. That is to keep increasing
    > /proc/sys/vm/min_free_kbytes until your allocation failures stop.

    We have developed a much more reliable workaround which works on both
    the 2.4 and 2.6 trees.

    Our development is called 'Pre-allocated Big Buffers', basically prebb
    provides fixed-sized pools of fixed-size blocks that are allocated during
    boot time using the bootmem allocator (thus are disconnected from the
    slab cache completely). block size need not to be page aligned. It is
    possible to allocate these blocks at O(1) efficiency at any context.

    Each pool has a minimum and maximum object size (where allocations
    should strive to be the maximum for memory usage efficiency). Currently
    we use prebb to ensure no fragmentation and fine-tuned memory usage.

    (Of course a few changes inside net/core/skbuff.c were needed for
    skb buffers to allocate from prebb instead of slab).

    --
    Dan Aloni
    da-x@monatomic.org, da-x@colinux.org, da-x@gmx.net
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