linux-kernel - Re: [PATCH 9/9] mm, page_alloc: optionally disable pcplists during page isolation

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Date:   Mon, 5 Oct 2020 16:22:46 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...e.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Oscar Salvador <osalvador@...e.de>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 9/9] mm, page_alloc: optionally disable pcplists during
 page isolation

On 10/5/20 4:05 PM, Michal Hocko wrote:
> On Fri 25-09-20 13:10:05, Vlastimil Babka wrote:
>> On 9/25/20 12:54 PM, David Hildenbrand wrote:
>>
>> Hmm that temporary write lock would still block new callers until previous
>> finish with the downgraded-to-read lock.
>>
>> But I guess something like this would work:
>>
>> retry:
>>   if (atomic_read(...) == 0) {
>>     // zone_update... + drain
>>     atomic_inc(...);
>>   else if (atomic_inc_return == 1)
>>     // atomic_cmpxchg from 0 to 1; if that fails, goto retry
>>
>> Tricky, but races could only read to unnecessary duplicated updates + flushing
>> but nothing worse?
>>
>> Or add another spinlock to cover this part instead of the temp write lock...
> 
> Do you plan to post a new version or should I review this one?

I will, hopefully this week, but you could comment on other details and
overall approach meanwhile? I don't think it will change significantly.