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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qLPpO-0041Jy-Fb; Mon, 17 Jul 2023 15:07:58 +0000 Date: Mon, 17 Jul 2023 16:07:58 +0100 From: Matthew Wilcox To: Ryan Roberts Cc: Andrew Morton , Yin Fengwei , David Hildenbrand , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v1 2/3] mm: Implement folio_remove_rmap_range() Message-ID: References: <20230717143110.260162-1-ryan.roberts@arm.com> <20230717143110.260162-3-ryan.roberts@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230717143110.260162-3-ryan.roberts@arm.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0E212A0113 X-Stat-Signature: 3jbq88nj98h9aekxc3483t3adx53qu8i X-HE-Tag: 1689606492-756905 X-HE-Meta: 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 UIaCNs2P +/sP0gZdKgh1637Fm0+kgKg2hqkLLpojRT6V0vBh2DM0pamfno4rcD65wrHpF+3IoErPVeTRB2xYO5zS2xSUu61CKzuUsGIFhS61gn9roLGNIKFz28lpMVECvmrU3FMzqochuRV6mMzQbKHlmYiYJaif7ahyvjPSY3yJNtoJXQ50M1NXoDfKbDOIBqA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 17, 2023 at 03:31:09PM +0100, Ryan Roberts wrote: > +/* > + * folio_remove_rmap_range - take down pte mappings from a range of pages > + * belonging to a folio. All pages are accounted as small pages. > + * @folio: folio that all pages belong to > + * @page: first page in range to remove mapping from > + * @nr: number of pages in range to remove mapping from > + * @vma: the vm area from which the mapping is removed > + * > + * The caller needs to hold the pte lock. > + */ This could stand a little reworking. How about this? /** * folio_remove_rmap_range - Take down PTE mappings from a range of pages. * @folio: Folio containing all pages in range. * @page: First page in range to unmap. * @nr: Number of pages to unmap. * @vma: The VM area containing the range. * * All pages in the range must belong to the same VMA & folio. They * must be mapped with PTEs, not a PMD. * * Context: Caller holds the pte lock. */ > +void folio_remove_rmap_range(struct folio *folio, struct page *page, > + int nr, struct vm_area_struct *vma) > +{ > + atomic_t *mapped = &folio->_nr_pages_mapped; > + int nr_unmapped = 0; > + int nr_mapped; > + bool last; > + enum node_stat_item idx; > + > + if (unlikely(folio_test_hugetlb(folio))) { > + VM_WARN_ON_FOLIO(1, folio); > + return; > + } > + > + if (!folio_test_large(folio)) { > + /* Is this the page's last map to be removed? */ > + last = atomic_add_negative(-1, &page->_mapcount); > + nr_unmapped = last; > + } else { > + for (; nr != 0; nr--, page++) { > + /* Is this the page's last map to be removed? */ > + last = atomic_add_negative(-1, &page->_mapcount); > + if (last) { > + /* Page still mapped if folio mapped entirely */ > + nr_mapped = atomic_dec_return_relaxed(mapped); We're still doing one atomic op per page on the folio's nr_pages_mapped ... is it possible to batch this and use atomic_sub_return_relaxed()?