Re: [LKML]kmalloc -contiguous locations ?

From: tabris (tabris_at_tabris.net)
Date: 06/01/04

  • Next message: Bernd Eckenfels: "Re: why swap at all?" 
    To: Shobhit Mathur <shobhitmmathur@yahoo.com>
Date:	Mon, 31 May 2004 19:24:00 -0400

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    On Monday 31 May 2004 5:49 am, Shobhit Mathur wrote:
    > Hello,
    >
    > I would like to know whether kmalloc() guarantees
    > virtually contiguous memory locations ?
    > Is there a limit on the amount of contiguous memory
    > that can be returned by kmalloc() ?
            First, kmalloc returns physically contiguous memory.
            second, the limit (on x86) is 128kb (32 pages), allocatable in powers of two
    pages. (1,2,4,8,16,32. often called 0-order thru 5-order allocations)

            vmalloc returns virtual contiguous allocations, with no guarantee on physical
    contiguity. The problem with vmalloc, iirc, is that there's a [total] limit
    of 128MB for vmallocs.

            Also remember that all kernel memory allocated with vmalloc() or kmalloc() is
    non-swappable.

            I don't know how this changes under any other architecture, such as x86-64 or
    PPC32/64.
    >
    > - Thank you
    >
    > - Shobhit Mathur

    - --
    tabris
    - -
            A master was explaining the nature of Tao to one of his novices.
    "The Tao is embodied in all software -- regardless of how insignificant,"
    said the master.
            "Is Tao in a hand-held calculator?" asked the novice.
            "It is," came the reply.
            "Is the Tao in a video game?" continued the novice.
            "It is even in a video game," said the master.
            "And is the Tao in the DOS for a personal computer?"
            The master coughed and shifted his position slightly. "The lesson
    is over for today," he said.
                    -- Geoffrey James, "The Tao of Programming"
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