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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id n20-20020a05620a153400b00759300a1ef9sm1270513qkk.31.2023.06.20.09.06.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jun 2023 09:06:17 -0700 (PDT) Date: Tue, 20 Jun 2023 12:06:15 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrea Arcangeli , Mike Rapoport , Matthew Wilcox , Vlastimil Babka , John Hubbard , "Kirill A . Shutemov" , James Houghton , Andrew Morton , Lorenzo Stoakes , Hugh Dickins , Mike Kravetz , Jason Gunthorpe Subject: Re: [PATCH v2 2/8] mm/hugetlb: Prepare hugetlb_follow_page_mask() for FOLL_PIN Message-ID: References: <20230619231044.112894-1-peterx@redhat.com> <20230619231044.112894-3-peterx@redhat.com> <7cd1db3f-9bdf-dc0b-692c-380a2fa14286@redhat.com> MIME-Version: 1.0 In-Reply-To: <7cd1db3f-9bdf-dc0b-692c-380a2fa14286@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Stat-Signature: r3xw67ihp614dd99zaxjb3dfc41aa81g X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 80F8A140090 X-Rspam-User: X-HE-Tag: 1687277184-177620 X-HE-Meta: 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 hWM4WnuX opqVAzZfvSC+RoU1fvKdbY1SibfSD8FtfqZ1KrgRRzTCoAWbHKjsZ2rcxnu4pTK2/XALV2CRHZb9w4gvGTEzOkg6sdd4aLXwRHMdA3oCZ9aFOxY+5GwIENqVnyrM7D+aV9Rhry0d0oF9fAE+Ttd1zNBUq/jIF43y822sdzWhOor+AJ6B6VUsi0v6b8A+gFj8NML+eHZ//SUH0n2Z0cqb4x3VfCulWpUCCJa6iJqs3/d+PpyGzap73WMFmxTyDSiV4crpBGcKUXv2y4uNZ17V4MIhLQPChK0+4b10OB9VCAZ0W7tgg+pkz6VadCjbm8fF4moTuKSCsChhJky95Ke9+uRS7/FWQcdjOxSgLUYFYYFlgexqiyaHrnJxMPzfZlCyZ9wnLbMWZTP5fXDN0ljp6K7wIhOeii8iW06dn 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 Tue, Jun 20, 2023 at 05:28:28PM +0200, David Hildenbrand wrote: > On 20.06.23 01:10, Peter Xu wrote: > > follow_page() doesn't use FOLL_PIN, meanwhile hugetlb seems to not be the > > target of FOLL_WRITE either. However add the checks. > > > > Namely, either the need to CoW due to missing write bit, or proper CoR on > > !AnonExclusive pages over R/O pins to reject the follow page. That brings > > this function closer to follow_hugetlb_page(). > > > > So we don't care before, and also for now. But we'll care if we switch > > over slow-gup to use hugetlb_follow_page_mask(). We'll also care when to > > return -EMLINK properly, as that's the gup internal api to mean "we should > > do CoR". Not really needed for follow page path, though. > > > > When at it, switching the try_grab_page() to use WARN_ON_ONCE(), to be > > clear that it just should never fail. > > Oh, and does this comment really belong into this patch or am I confused? Ah yeh, thanks for spotting. I used to have it in v1 but I kept the old failure path here to partly address Lorenzo's worry; but then I forgot to add the WARN_ON_ONCE back to guard. I'll remember to add that in v3. -- Peter Xu