linux-kernel - Re: [RFC PATCH v2 12/47] hugetlb: add hugetlb_hgm_walk and hugetlb_walk

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Message-ID: <CADrL8HXY_U1Ag2BnAv11gsMw_6EccDqSg7u6hd=9ws_J3z0cyg@mail.gmail.com>
Date:   Wed, 16 Nov 2022 17:39:12 -0800
From:   James Houghton <jthoughton@...gle.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        "Zach O'Keefe" <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 12/47] hugetlb: add hugetlb_hgm_walk and hugetlb_walk_step

On Wed, Nov 16, 2022 at 2:02 PM Peter Xu <peterx@...hat.com> wrote:
>
> On Fri, Oct 21, 2022 at 04:36:28PM +0000, James Houghton wrote:
> > +/* hugetlb_hgm_walk - walks a high-granularity HugeTLB page table to resolve
> > + * the page table entry for @addr.
> > + *
> > + * @hpte must always be pointing at an hstate-level PTE (or deeper).
> > + *
> > + * This function will never walk further if it encounters a PTE of a size
> > + * less than or equal to @sz.
> > + *
> > + * @stop_at_none determines what we do when we encounter an empty PTE.
>
> IIUC it is not about empty PTE but swap-or-empty pte?
>
> I'm not sure whether it'll be more straightforward to have "bool alloc"
> just to show whether the caller would like to allocate pgtables when
> walking the sub-level pgtable until the level specified.

I think "bool alloc" is cleaner. I'll do that. Thanks for the suggestion.

>
> In final version of the code I also think we should drop all the "/*
> stop_at_pte */" comments in the callers. Maybe that already means the
> meaning of the bool is confusing so we always need a hint.

I did that to hopefully make things easier to read. I'll remove it.

- James

>
> --
> Peter Xu
>