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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id t8sm18958766wrp.69.2020.01.14.01.25.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jan 2020 01:25:47 -0800 (PST) Date: Tue, 14 Jan 2020 10:25:45 +0100 From: Michal Hocko To: Li Xinhai Cc: linux-mm@kvack.org, akpm@linux-foundation.org, "Kirill A. Shutemov" , Mike Kravetz Subject: Re: [PATCH v4] mm/page_vma_mapped.c: Explicitly compare pfn for normal, hugetlbfs and THP page Message-ID: <20200114092545.GF19428@dhcp22.suse.cz> References: <1578737885-8890-1-git-send-email-lixinhai.lxh@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1578737885-8890-1-git-send-email-lixinhai.lxh@gmail.com> User-Agent: Mutt/1.12.2 (2019-09-21) 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 Sat 11-01-20 10:18:05, Li Xinhai wrote: > When check_pte, pfn of normal, hugetlbfs and THP page need be compared. > The current implementation apply comparison as > - normal 4K page: page_pfn <= pfn < page_pfn + 1 > - hugetlbfs page: page_pfn <= pfn < page_pfn + HPAGE_PMD_NR > - THP page: page_pfn <= pfn < page_pfn + HPAGE_PMD_NR > in pfn_in_hpage. For hugetlbfs page, it should be > page_pfn == pfn > > Now, change pfn_in_hpage to pfn_is_match to highlight that comparison > is not only for THP and explicitly compare for these cases. Why is this important to do. I have asked and Mike had the same feeling that the patch is missing any real justification. Why do we need this change? It is great that you have dropped VM_BUG_ON btw. > Signed-off-by: Li Xinhai > Cc: Kirill A. Shutemov > Cc: Mike Kravetz > Cc: Michal Hocko > Acked-by: Kirill A. Shutemov > --- > mm/page_vma_mapped.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index eff4b45..719c352 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -52,12 +52,16 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) > return true; > } > > -static inline bool pfn_in_hpage(struct page *hpage, unsigned long pfn) > +static inline bool pfn_is_match(struct page *page, unsigned long pfn) > { > - unsigned long hpage_pfn = page_to_pfn(hpage); > + unsigned long page_pfn = page_to_pfn(page); > + > + /* normal page and hugetlbfs page */ > + if (!PageTransCompound(page) || PageHuge(page)) > + return page_pfn == pfn; > > /* THP can be referenced by any subpage */ > - return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage); > + return pfn >= page_pfn && pfn - page_pfn < hpage_nr_pages(page); > } > > /** > @@ -108,7 +112,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw) > pfn = pte_pfn(*pvmw->pte); > } > > - return pfn_in_hpage(pvmw->page, pfn); > + return pfn_is_match(pvmw->page, pfn); > } > > /** > -- > 1.8.3.1 -- Michal Hocko SUSE Labs