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    SubjectRe: [PATCH 2/2] block: Avoid deadlocks with bio allocation by stacking drivers
    From
    Kent,

    On Tue, Sep 11, 2012 at 12:31 PM, Kent Overstreet
    <koverstreet@google.com> wrote:
    > On Tue, Sep 11, 2012 at 11:58:05AM -0700, Muthu Kumar wrote:
    >> On Tue, Sep 11, 2012 at 11:45 AM, Tejun Heo <tj@kernel.org> wrote:
    >> > Hello,
    >> >
    >> > On Tue, Sep 11, 2012 at 11:36:28AM -0700, Muthu Kumar wrote:
    >> >> Does this preserve the CPU from which the bio was submitted
    >> >> originally. Not familiar with cmwq, may be Tejun can clarify.
    >> >>
    >> >> Tejun - the question is, do we honor the rq_affinity with the above
    >> >> rescue worker implementation?
    >> >
    >> > The work item would run from the same CPU but there isn't any
    >> > mechanism to keep track of the issuing CPU if there are multiple bios
    >> > to be rescued. Isn't rq_affinity an optimization hint? If so, I
    >> > don't think it matters here.
    >> >
    >>
    >> Thanks... Just worried about performance impact.
    >>
    >> Kent - Anything to validate that the performance is not impacted would
    >> be really good. Otherwise, the patch looks great.
    >
    > Well - there'll only be any performance impact at all when we're memory
    > constrained enough that GFP_NOWAIT allocations fail, which for these
    > size allocations definitely isn't normal.


    Agreed. If we are in this situation, we are already running in
    degraded mode. So performance is not in question.

    Regards,
    Muthu


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