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Shutemov" Cc: Wei Yang , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm/page_vma_mapped: use PMD_SIZE instead of calculating it Message-ID: <20191128212226.sfrhfs5m3q7m6tly@master> Reply-To: Wei Yang References: <20191128010321.21730-1-richardw.yang@linux.intel.com> <20191128083255.ab5rwj7gvktwunik@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191128083255.ab5rwj7gvktwunik@box.shutemov.name> User-Agent: NeoMutt/20170113 (1.7.2) 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 Thu, Nov 28, 2019 at 11:32:55AM +0300, Kirill A. Shutemov wrote: >On Thu, Nov 28, 2019 at 09:03:20AM +0800, Wei Yang wrote: >> At this point, we are sure page is PageTransHuge, which means >> hpage_nr_pages is HPAGE_PMD_NR. >> >> This is safe to use PMD_SIZE instead of calculating it. >> >> Signed-off-by: Wei Yang >> --- >> mm/page_vma_mapped.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >> index eff4b4520c8d..76e03650a3ab 100644 >> --- a/mm/page_vma_mapped.c >> +++ b/mm/page_vma_mapped.c >> @@ -223,7 +223,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >> if (pvmw->address >= pvmw->vma->vm_end || >> pvmw->address >= >> __vma_address(pvmw->page, pvmw->vma) + >> - hpage_nr_pages(pvmw->page) * PAGE_SIZE) >> + PMD_SIZE) >> return not_found(pvmw); >> /* Did we cross page table boundary? */ >> if (pvmw->address % PMD_SIZE == 0) { > >It is dubious cleanup. Maybe page_size(pvmw->page) instead? It will not >break if we ever get PUD THP pages. > Thanks for your comment. I took a look into the code again and found I may miss something. I found we support PUD THP pages, whilc hpage_nr_pages() just return HPAGE_PMD_NR on PageTransHuge. Why this is not possible to return PUD number? Search in the kernel tree, one implementation of PUD_SIZE fault is dev_dax_huge_fault. If page fault happens here, would this if break the loop too early? >-- > Kirill A. Shutemov -- Wei Yang Help you, Help me