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Date:   Tue, 10 Aug 2021 11:29:11 +0200
From:   Oscar Salvador <osalvador@suse.de>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Muchun Song <songmuchun@bytedance.com>,
        Michal Hocko <mhocko@suse.com>,
        David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Mina Almasry <almasrymina@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 1/3] hugetlb: simplify prep_compound_gigantic_page ref
 count racing code
In-Reply-To: <20210809184832.18342-2-mike.kravetz@oracle.com>
References: <20210809184832.18342-1-mike.kravetz@oracle.com>
 <20210809184832.18342-2-mike.kravetz@oracle.com>
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On 2021-08-09 20:48, Mike Kravetz wrote:
> Code in prep_compound_gigantic_page waits for a rcu grace period if it
> notices a temporarily inflated ref count on a tail page.  This was due
> to the identified potential race with speculative page cache references
> which could only last for a rcu grace period.  This is overly 
> complicated
> as this situation is VERY unlikely to ever happen.  Instead, just 
> quickly
> return an error.
> Also, only print a warning in prep_compound_gigantic_page instead of
> multiple callers.

The above makes sense to me.
My only question would be: gather_bootmem_prealloc() is an __init 
function.
Can we have speculative refcounts due to e.g: pagecache at that early 
stage?
I think we cannot, but I am not really sure.

We might be able to remove that else() in case we cannot have such 
scenarios.


-- 
Oscar Salvador
SUSE L3