linux-kernel - Re: [RFC PATCH 04/26] hugetlb: make huge_pte_lockptr take an explicit shift argument.

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Date:   Mon, 27 Jun 2022 13:51:53 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     James Houghton <jthoughton@...gle.com>
Cc:     Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Jue Wang <juew@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 04/26] hugetlb: make huge_pte_lockptr take an
 explicit shift argument.

On 06/24/22 17:36, James Houghton wrote:
> This is needed to handle PTL locking with high-granularity mapping. We
> won't always be using the PMD-level PTL even if we're using the 2M
> hugepage hstate. It's possible that we're dealing with 4K PTEs, in which
> case, we need to lock the PTL for the 4K PTE.

I'm not really sure why this would be required.
Why not use the PMD level lock for 4K PTEs?  Seems that would scale better
with less contention than using the more coarse mm lock.  

-- 
Mike Kravetz