linux-kernel - Re: Memory hotplug softlock issue

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Date:   Wed, 14 Nov 2018 10:39:06 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Baoquan He <bhe@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        aarcange@...hat.com
Subject: Re: Memory hotplug softlock issue

>>> Failing on ENOMEM is a questionable thing. I haven't seen that happening
>>> wildly but if it is a case then I wouldn't be opposed.
>>>
>>>> You mentioned memory pressure, if our host is under memory pressure we
>>>> can easily trigger running into an endless loop there, because we
>>>> basically ignore -ENOMEM e.g. when we cannot get a page to migrate some
>>>> memory to be offlined. I assume this is the case here.
>>>> do_migrate_range() could be the bad boy if it keeps failing forever and
>>>> we keep retrying.
>>
>> I've seen quite some issues while playing with virtio-mem, but didn't
>> have the time to look into the details. Still on my long list of things
>> to look into.
> 
> Memory hotplug is really far away from being optimal and robust. This
> has always been the case. Issues used to be workaround by retry limits
> etc. If we ever want to make it more robust we have to bite a bullet and
> actually chase all the issues that might be basically anywhere and fix
> them. This is just a nature of a pony that memory hotplug is.
> 

Yes I agree, no more workarounds.

-- 

Thanks,

David / dhildenb