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    SubjectRe: [PATCH 5/8] cfq-iosched: remove @gfp_mask from cfq_find_alloc_queue()
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    Jeff Moyer <jmoyer@redhat.com> writes:

    > Tejun Heo <tj@kernel.org> writes:
    >
    >> Even when allocations fail, cfq_find_alloc_queue() always returns a
    >> valid cfq_queue by falling back to the oom cfq_queue. As such, there
    >> isn't much point in taking @gfp_mask and trying "harder" if __GFP_WAIT
    >> is set. GFP_ATOMIC allocations don't fail often and even when they do
    >> the degraded behavior is acceptable and temporary.
    >>
    >> After all, the only reason get_request(), which ultimately determines
    >> the gfp_mask, cares about __GFP_WAIT is to guarantee request
    >> allocation, assuming IO forward progress, for callers which are
    >> willing to wait. There's no reason for cfq_find_alloc_queue() to
    >> behave differently on __GFP_WAIT when it already has a fallback
    >> mechanism.
    >>
    >> Remove @gfp_mask from cfq_find_alloc_queue() and propagate the changes
    >> to its callers. This simplifies the function quite a bit and will
    >> help making async queues per-cfq_group.
    >
    > Sorry, I disagree with this patch. You've changed it so that all cfqq
    > allocations are GFP_ATOMIC, and most, if not all of them simply don't
    > need to be.

    It occurs to me that replacing GFP_ATOMIC with GFP_NOWAIT in your patch
    would address my concerns, and patches 6-8 would apply almost as-is.
    What do you think about that?

    -Jeff


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