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    mm, oom: distinguish blockable mode for mmu notifiers · 93065ac7
    Michal Hocko 提交于
    There are several blockable mmu notifiers which might sleep in
    mmu_notifier_invalidate_range_start and that is a problem for the
    oom_reaper because it needs to guarantee a forward progress so it cannot
    depend on any sleepable locks.
    
    Currently we simply back off and mark an oom victim with blockable mmu
    notifiers as done after a short sleep.  That can result in selecting a new
    oom victim prematurely because the previous one still hasn't torn its
    memory down yet.
    
    We can do much better though.  Even if mmu notifiers use sleepable locks
    there is no reason to automatically assume those locks are held.  Moreover
    majority of notifiers only care about a portion of the address space and
    there is absolutely zero reason to fail when we are unmapping an unrelated
    range.  Many notifiers do really block and wait for HW which is harder to
    handle and we have to bail out though.
    
    This patch handles the low hanging fruit.
    __mmu_notifier_invalidate_range_start gets a blockable flag and callbacks
    are not allowed to sleep if the flag is set to false.  This is achieved by
    using trylock instead of the sleepable lock for most callbacks and
    continue as long as we do not block down the call chain.
    
    I think we can improve that even further because there is a common pattern
    to do a range lookup first and then do something about that.  The first
    part can be done without a sleeping lock in most cases AFAICS.
    
    The oom_reaper end then simply retries if there is at least one notifier
    which couldn't make any progress in !blockable mode.  A retry loop is
    already implemented to wait for the mmap_sem and this is basically the
    same thing.
    
    The simplest way for driver developers to test this code path is to wrap
    userspace code which uses these notifiers into a memcg and set the hard
    limit to hit the oom.  This can be done e.g.  after the test faults in all
    the mmu notifier managed memory and set the hard limit to something really
    small.  Then we are looking for a proper process tear down.
    
    [akpm@linux-foundation.org: coding style fixes]
    [akpm@linux-foundation.org: minor code simplification]
    Link: http://lkml.kernel.org/r/20180716115058.5559-1-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com>
    Acked-by: Christian König <christian.koenig@amd.com> # AMD notifiers
    Acked-by: Leon Romanovsky <leonro@mellanox.com> # mlx and umem_odp
    Reported-by: NDavid Rientjes <rientjes@google.com>
    Cc: "David (ChunMing) Zhou" <David1.Zhou@amd.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Alex Deucher <alexander.deucher@amd.com>
    Cc: David Airlie <airlied@linux.ie>
    Cc: Jani Nikula <jani.nikula@linux.intel.com>
    Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
    Cc: Doug Ledford <dledford@redhat.com>
    Cc: Jason Gunthorpe <jgg@ziepe.ca>
    Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
    Cc: Dennis Dalessandro <dennis.dalessandro@intel.com>
    Cc: Sudeep Dutt <sudeep.dutt@intel.com>
    Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
    Cc: Dimitri Sivanich <sivanich@sgi.com>
    Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: "Jérôme Glisse" <jglisse@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Felix Kuehling <felix.kuehling@amd.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    93065ac7
kvm_main.c 95.7 KB