Re: Active Memory Defragmentation: Our implementation & problems

From: Dave McCracken (dmccr_at_us.ibm.com)
Date: 02/04/04

  • Next message: Valdis.Kletnieks_at_vt.edu: "Re: Kernel 2.x POSIX Compliance/Conformance..." 
    Date:	Wed, 04 Feb 2004 13:35:54 -0600
To: root@chaos.analogic.com

    --On Wednesday, February 04, 2004 14:07:52 -0500 "Richard B. Johnson"
    <root@chaos.analogic.com> wrote:

    > If this is an Intel x86 machine, it is impossible for pages
    > to get fragmented in the first place. The hardware allows any
    > page, from anywhere in memory, to be concatenated into linear
    > virtual address space. Even the kernel address space is virtual.
    > The only time you need physically-adjacent pages is if you
    > are doing DMA that is more than a page-length at a time. The
    > kernel keeps a bunch of those pages around for just that
    > purpose.
    >
    > So, if you are making a "memory defragmenter", it is a CPU time-sink.

    Um, wrong answer. When you ask for more than one page from the buddy
    allocator (order greater than 0) it always returns physically contiguous
    pages.

    Also, one of the near-term goals in VM is to be able to allocate and free
    large pages from the main memory pools, which requires that something like
    order 9 or 10 allocations (based on the architecture) succeed.

    Dave McCracken

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

  • Next message: Valdis.Kletnieks_at_vt.edu: "Re: Kernel 2.x POSIX Compliance/Conformance..."

    Relevant Pages

    • Re: p_vmspace in syscall
      ... In general, I prefer mapping user pages into kernel instead of kernel pages into user space, as it reduces the chances of leakage of kernel data to user space, and there are some useful primitives for making this easier. ... map the buffer to user process ... The pages allocated by mallocbelong to the kernel memory allocator, and are generally managed by the slab allocator. ...
      (freebsd-hackers)
    • Re: Q: HP-UX 11.31 slow performance without load
      ... Before the patch the kernel used to hang or crash. ... Which means that we're likely to have physical memory -- just not the ... Being inode related... ... It suggests you caused some memory to get flushed down to the allocator ...
      (comp.sys.hp.hpux)
    • Re: [RFC][PATCH 0/9] Network receive deadlock prevention for NBD
      ... hack openssh code to be able to allow it to use reserve when there is not enough memory. ... kernel services, and the continued well being of the kernel, not ... And even if you will cover all kernel-only network allocations, ... but if allocator depends on main system's memory ...
      (Linux-Kernel)
    • Re: [ckrm-tech] RFC: Memory Controller
      ... When one maps file then kernel can remove page from address ... Yes, I agree if there is no swap space, then anonymous memory is pinned. ... kmemsize hooks are the most "conservative" - only one place ... is heavily patched - this is slab allocator. ...
      (Linux-Kernel)
    • Re: Oops with 2.4.23
      ... First, the memory timings ... the kernel didn't have erratta fixes and workarounds that MS ... (Even though mine passed standard ... send the line "unsubscribe linux-kernel" in ...
      (Linux-Kernel)