linux-kernel - Re: [PATCH v2 1/3] mm: hugetlb: disable freeing vmemmap pages when struct page crosses page boundaries

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Date:   Wed, 2 Mar 2022 13:21:49 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        keescook@...omium.org, yzaikin@...gle.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com,
        Adam Manzanares <a.manzanares@...sung.com>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH v2 1/3] mm: hugetlb: disable freeing vmemmap pages when
 struct page crosses page boundaries

On Wed, Mar 02, 2022 at 04:37:56PM +0800, Muchun Song wrote:
> If CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON is enabled and the size
> of "struct page" is not power of two, we cannot optimize vmemmap pages
> of HugeTLB pages. We should disable this feature in this case.

The commit log does not descrie what happens if this is left enabled in
that case? Is this a fix? Why would it be a fix? Was something failing?
How did you spot this issue? What are the consequences of not applying
this patch?

  Luis