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Date:   Thu, 7 Nov 2019 18:04:56 -0800
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Waiman Long <longman@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] hugetlbfs: Take read_lock on i_mmap for PMD sharing
Message-ID: <20191108020456.sulyjskhq3s5zcaa@linux-p48b>
Mail-Followup-To: Mike Kravetz <mike.kravetz@oracle.com>,
        Matthew Wilcox <willy@infradead.org>,
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        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>
References: <20191107190628.22667-1-longman@redhat.com>
 <20191107195441.GF11823@bombadil.infradead.org>
 <ed46ef09-7766-eb80-a4ad-4c72d8dba188@oracle.com>
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On Thu, 07 Nov 2019, Mike Kravetz wrote:

>Note that huge_pmd_share now increments the page count with the semaphore
>held just in read mode.  It is OK to do increments in parallel without
>synchronization.  However, we don't want anyone else changing the count
>while that check in huge_pmd_unshare is happening.  Hence, the need for
>taking the semaphore in write mode.

This would be a nice addition to the changelog methinks.

Thanks,
Davidlohr