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    SubjectRe: [PATCH] perf_events: improve DS/BTS/PEBS buffer allocation
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    On Mon, Sep 13, 2010 at 5:08 PM, Peter Zijlstra <peterz@infradead.org> wrote:
    > On Mon, 2010-09-13 at 16:55 +0200, Stephane Eranian wrote:
    >> The DS, BTS, and PEBS memory regions were allocated using kzalloc(), i.e.,
    >> requesting contiguous physical memory. There is no such restriction on
    >> DS, PEBS and BTS buffers. Using kzalloc() could lead to error in case
    >> no contiguous physical memory is available. BTS is requesting 64KB,
    >> thus it can cause issues. PEBS is currently only requesting one page.
    >> Both PEBS and BTS are static buffers allocated for each CPU at the
    >> first user. When the last user exists, the buffers are released.
    >>
    >> All buffers are only accessed on the CPU they are attached to.
    >> kzalloc() does not take into account NUMA, thus all allocations
    >> are taking place on the NUMA node where the perf_event_open() is
    >> made.
    >
    > I guess that should have been a alloc_pages_node() indeed.
    >
    >> This patch switches allocation to vmalloc_node() to use non-contiguous
    >> physical memory and to allocate on the NUMA node corresponding to each
    >> CPU. We switched DS and PEBS although they do not cause problems today,
    >> to, at least, make the allocation on the correct NUMA node. In the future,
    >> the PEBS buffer size may increase. DS may also grow bigger than a page.
    >> This patch eliminates the memory allocation imbalance.
    >
    > I'm not really a fan of vmalloc, have you actually observed allocation
    > failures for these 64k (order-4) allocations?
    >
    I did with small amount of memory in containers, after stressing
    the system with perf for instance.

    >
    >


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