From: Matthew Wilcox <willy@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Zhang Yi <wetpzy@gmail.com>,
Mel Gorman <mgorman@techsingularity.net>,
Mike Kravetz <mike.kravetz@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Neel Natu <neelnatu@google.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm, futex: Fix shared futex pgoff on shmem huge page
Date: Sat, 12 Jun 2021 17:15:49 +0100 [thread overview]
Message-ID: <YMTdtRZG+7q8OtkK@casper.infradead.org> (raw)
In-Reply-To: <45e8fd67-51fd-7828-fe43-d261d6c33727@google.com>
On Fri, Jun 11, 2021 at 09:31:16PM -0700, Hugh Dickins wrote:
> +++ linux/include/linux/pagemap.h 2021-06-11 17:30:28.726720252 -0700
> @@ -516,8 +516,7 @@ static inline struct page *read_mapping_
> }
>
> /*
> - * Get index of the page with in radix-tree
> - * (TODO: remove once hugetlb pages will have ->index in PAGE_SIZE)
> + * Get index of the page within radix-tree (but not for hugetlb pages).
> */
I think the TODO should be retained. It's still something that I
intend to do.
> static inline pgoff_t page_to_pgoff(struct page *page)
> {
> - if (unlikely(PageHeadHuge(page)))
> - return page->index << compound_order(page);
> -
> + if (unlikely(PageHuge(page))) {
> + extern pgoff_t hugetlb_basepage_index(struct page *page);
> + return hugetlb_basepage_index(page);
> + }
> return page_to_index(page);
> }
Yes, this change absolutely makes sense. It's just a landmine if it
returns the right answer for some tail pages but garbage for other
kinds of tail pages.
> --- 5.13-rc5/mm/hugetlb.c 2021-06-06 16:57:26.263006733 -0700
> +++ linux/mm/hugetlb.c 2021-06-11 17:30:28.730720276 -0700
> @@ -1588,15 +1588,12 @@ struct address_space *hugetlb_page_mappi
> return NULL;
> }
>
> -pgoff_t __basepage_index(struct page *page)
> +pgoff_t hugetlb_basepage_index(struct page *page)
> {
> struct page *page_head = compound_head(page);
> pgoff_t index = page_index(page_head);
> unsigned long compound_idx;
>
> - if (!PageHuge(page_head))
> - return page_index(page);
> -
> if (compound_order(page_head) >= MAX_ORDER)
> compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
> else
>
urgh. this trailing bit should be:
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
#else
compound_idx = page - page_head;
#endif
next prev parent reply other threads:[~2021-06-12 16:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-12 4:31 [PATCH] mm, futex: Fix shared futex pgoff on shmem huge page Hugh Dickins
2021-06-12 16:15 ` Matthew Wilcox [this message]
2021-06-13 3:14 ` Hugh Dickins
2021-06-13 3:16 ` [PATCH v2] " Hugh Dickins
2021-06-13 10:27 ` Matthew Wilcox
2021-06-15 14:53 ` Thomas Gleixner
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