linux-kernel - Re: [PATCH RFC 06/12] mm/gup: Drop folio_fast_pin

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Message-ID: <ZV95WMqoZzchrcBY@x1n>
Date:   Thu, 23 Nov 2023 11:10:00 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        James Houghton <jthoughton@...gle.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        Yang Shi <shy828301@...il.com>,
        Rik van Riel <riel@...riel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, Mike Rapoport <rppt@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: Re: [PATCH RFC 06/12] mm/gup: Drop folio_fast_pin_allowed() in
 hugepd processing

On Wed, Nov 22, 2023 at 11:21:50PM -0800, Christoph Hellwig wrote:
> That alone sounds like a good reason to not bother.  So unless more
> qualified people have a different opinion I'm fine with this patch
> as long as you leave a comment in place, and ammend the commit message
> with some of the very useful information from your mail.

Will do, thanks.

This is what I will squash into the same patch in the new version, as the
current plan:

+/*
+ * NOTE: currently hugepd is only used in hugetlbfs file systems on Power,
+ * which does not have issue with folio writeback against GUP updates.
+ * When hugepd will be extended to support non-hugetlbfs or even anonymous
+ * memory, we need to do extra check as what we do with most of the other
+ * folios. See writable_file_mapping_allowed() and folio_fast_pin_allowed()
+ * for more information.
+ */
static int gup_huge_pd(hugepd_t hugepd, unsigned long addr,
                unsigned int pdshift, unsigned long end, unsigned int flags,
                struct page **pages, int *nr)

-- 
Peter Xu