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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id i10-20020ac860ca000000b003f9cca00552sm238782qtm.93.2023.06.19.13.24.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 19 Jun 2023 13:24:32 -0700 (PDT) Date: Mon, 19 Jun 2023 16:24:31 -0400 From: Peter Xu To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox , Andrea Arcangeli , John Hubbard , Mike Rapoport , David Hildenbrand , Vlastimil Babka , "Kirill A . Shutemov" , Andrew Morton , Mike Kravetz , James Houghton , Hugh Dickins Subject: Re: [PATCH 6/7] mm/gup: Accelerate thp gup even for "pages != NULL" Message-ID: References: <20230613215346.1022773-1-peterx@redhat.com> <20230613215346.1022773-7-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Stat-Signature: 8873paf6o9ka9dcjwxbt8qbrxep5bt6c X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 86E83C0002 X-Rspam-User: X-HE-Tag: 1687206276-867404 X-HE-Meta: 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 Km14YOYt 8qnKRyhstnl4sFx4dJuzNoM8WpAweDUSeUMuJXF8AgzfsYRp9iRo7I/9mML8B7r9T2od4Y/CXbjnaa9U1F7rni6i0UXQWGSoPAubFm87Xj4ZibpWIeRx5KnQrV2kGo1AkEHhYc5KAtYG933TOOO5SBTLl2pswxDuSxMnhDCQuvzuhEyKCTud+ifjq6UutIqXEPAfOuEXkg3Pcfs0jAZfsU+rGDrTJ9/87ZvbECZZJSpick2DEzBG5Yo/2JlvlqbXzFUxmgqOzCp1BZVzDh/Srr08AU2Qiz/bdsnrGVQYN/NBBcsJpTaXRYERFW3gcxRwKdQPLsdwOEjEsOFzipyW5mwELb9QxN0vyMYNoGHP6tRN416NzihkdxpYm33m1Mxv3TBa014QjJLn+MU9URq/H6D944g== 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, Jun 19, 2023 at 03:37:30PM -0400, Peter Xu wrote: > Here what I can do is still guard this try_grab_folio() and fail the GUP if > for any reason it failed. Perhaps then it means I'll also keep that one > untouched in hugetlb_follow_page_mask() too. But I suppose keeping the > WARN_ON_ONCE() seems still proper. Here's the outcome that I plan to post in the new version, taking care of try_grab_folio() failures even if it happens, meanwhile remove the compound_head() redundancy on the page. __get_user_pages(): ... ===8<=== /* * This must be a large folio (and doesn't need to * be the whole folio; it can be part of it), do * the refcount work for all the subpages too. * * NOTE: here the page may not be the head page * e.g. when start addr is not thp-size aligned. * try_grab_folio() should have taken care of tail * pages. */ if (page_increm > 1) { struct folio *folio; /* * Since we already hold refcount on the * large folio, this should never fail. */ folio = try_grab_folio(page, page_increm - 1, foll_flags); if (WARN_ON_ONCE(!folio)) { /* * Release the 1st page ref if the * folio is problematic, fail hard. */ gup_put_folio(page_folio(page), 1, foll_flags); ret = -EFAULT; goto out; } } ===8<=== Thanks, -- Peter Xu