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

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Message-ID: <20201005165651.GG4555@dhcp22.suse.cz>
Date:   Mon, 5 Oct 2020 18:56:51 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vlastimil Babka <vbabka@...e.cz>
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 Mon 05-10-20 16:22:46, Vlastimil Babka wrote:
> 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.

OK. I will have a look tomorrow.

-- 
Michal Hocko
SUSE Labs