linux-kernel - Re: [PATCH v3 10/11] mm/memory_hotplug: Make unregister_memory_block_under

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Date:   Mon, 15 Jul 2019 13:10:33 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>,
        Oscar Salvador <osalvador@...e.de>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        Dan Williams <dan.j.williams@...el.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Igor Mammedov <imammedo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Mark Brown <broonie@...nel.org>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v3 10/11] mm/memory_hotplug: Make
 unregister_memory_block_under_nodes() never fail

On 01.07.19 12:27, Michal Hocko wrote:
> On Mon 01-07-19 11:36:44, Oscar Salvador wrote:
>> On Mon, Jul 01, 2019 at 10:51:44AM +0200, Michal Hocko wrote:
>>> Yeah, we do not allow to offline multi zone (node) ranges so the current
>>> code seems to be over engineered.
>>>
>>> Anyway, I am wondering why do we have to strictly check for already
>>> removed nodes links. Is the sysfs code going to complain we we try to
>>> remove again?
>>
>> No, sysfs will silently "fail" if the symlink has already been removed.
>> At least that is what I saw last time I played with it.
>>
>> I guess the question is what if sysfs handling changes in the future
>> and starts dropping warnings when trying to remove a symlink is not there.
>> Maybe that is unlikely to happen?
> 
> And maybe we handle it then rather than have a static allocation that
> everybody with hotremove configured has to pay for.
> 

So what's the suggestion? Dropping the nodemask_t completely and calling
sysfs_remove_link() on already potentially removed links?

Of course, we can also just use mem_blk->nid and rest assured that it
will never be called for memory blocks belonging to multiple nodes.

-- 

Thanks,

David / dhildenb