Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220624173656.2033256-1-jthoughton@google.com>
 <20220624173656.2033256-5-jthoughton@google.com> <YroYaWVvNZJvtqsH@monkey>
In-Reply-To: <YroYaWVvNZJvtqsH@monkey>
From:   James Houghton <jthoughton@google.com>
Date:   Tue, 28 Jun 2022 08:29:25 -0700
Message-ID: <CADrL8HXoKUP3Fjb-R1-YL0JWohG23BtgiBTFdijK_LYPA8-0-g@mail.gmail.com>
Subject: Re: [RFC PATCH 04/26] hugetlb: make huge_pte_lockptr take an explicit
 shift argument.
To:     Mike Kravetz <mike.kravetz@oracle.com>
Cc:     Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>,
        David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Jue Wang <juew@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Jun 27, 2022 at 1:52 PM Mike Kravetz <mike.kravetz@oracle.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