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Fri, 13 Jun 2025 14:01:57 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id W9rjJlUvTGinDgAAD6G6ig (envelope-from ); Fri, 13 Jun 2025 14:01:57 +0000 Date: Fri, 13 Jun 2025 16:01:47 +0200 From: Oscar Salvador To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, Andrew Morton , Alistair Popple , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Dan Williams , Jason Gunthorpe Subject: Re: [PATCH v3 3/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pud() Message-ID: References: <20250613092702.1943533-1-david@redhat.com> <20250613092702.1943533-4-david@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250613092702.1943533-4-david@redhat.com> X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MISSING_XM_UA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[20]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,nvidia.com:email] X-Spam-Level: X-Spam-Flag: NO X-Spam-Score: -4.30 On Fri, Jun 13, 2025 at 11:27:02AM +0200, David Hildenbrand wrote: > Marking PUDs that map a "normal" refcounted folios as special is > against our rules documented for vm_normal_page(). normal (refcounted) > folios shall never have the page table mapping marked as special. > > Fortunately, there are not that many pud_special() check that can be > mislead and are right now rather harmless: e.g., none so far > bases decisions whether to grab a folio reference on that decision. > > Well, and GUP-fast will fallback to GUP-slow. All in all, so far no big > implications as it seems. > > Getting this right will get more important as we introduce > folio_normal_page_pud() and start using it in more place where we > currently special-case based on other VMA flags. > > Fix it just like we fixed vmf_insert_folio_pmd(). > > Add folio_mk_pud() to mimic what we do with folio_mk_pmd(). > > Fixes: dbe54153296d ("mm/huge_memory: add vmf_insert_folio_pud()") > Reviewed-by: Dan Williams > Reviewed-by: Lorenzo Stoakes > Reviewed-by: Jason Gunthorpe > Tested-by: Dan Williams > Signed-off-by: David Hildenbrand Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE Labs