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

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Date:   Tue, 28 Jun 2022 08:29:25 -0700
From:   James Houghton <jthoughton@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.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 Mon, Jun 27, 2022 at 1:52 PM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> 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.

I should be using the PMD level lock for 4K PTEs, yeah. I'll work this
into the next version of the series. Thanks both.

>
> --
> Mike Kravetz