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    SubjectRe: [patch 00/12] mm: page_alloc: improve OOM mechanism and policy
    On Wed, Apr 01, 2015 at 05:19:20PM +0200, Michal Hocko wrote:
    > On Mon 30-03-15 11:32:40, Dave Chinner wrote:
    > > On Fri, Mar 27, 2015 at 11:05:09AM -0400, Johannes Weiner wrote:
    > [...]
    > > > GFP_NOFS sites are currently one of the sites that can deadlock inside
    > > > the allocator, even though many of them seem to have fallback code.
    > > > My reasoning here is that if you *have* an exit strategy for failing
    > > > allocations that is smarter than hanging, we should probably use that.
    > >
    > > We already do that for allocations where we can handle failure in
    > > GFP_NOFS conditions. It is, however, somewhat useless if we can't
    > > tell the allocator to try really hard if we've already had a failure
    > > and we are already in memory reclaim conditions (e.g. a shrinker
    > > trying to clean dirty objects so they can be reclaimed).
    > >
    > > From that perspective, I think that this patch set aims force us
    > > away from handling fallbacks ourselves because a) it makes GFP_NOFS
    > > more likely to fail, and b) provides no mechanism to "try harder"
    > > when we really need the allocation to succeed.
    > You can ask for this "try harder" by __GFP_HIGH flag. Would that help
    > in your fallback case?

    That dips into GFP_ATOMIC reserves, right? What is the impact on the
    GFP_ATOMIC allocations that need it? We typically see network cards
    fail GFP_ATOMIC allocations before XFS starts complaining about
    allocation failures, so i suspect that this might just make things
    worse rather than better...


    Dave Chinner

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