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Fri, 13 Jun 2025 13:49:56 +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 ng2tMoQsTGhFCwAAD6G6ig (envelope-from ); Fri, 13 Jun 2025 13:49:56 +0000 Date: Fri, 13 Jun 2025 15:49:46 +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 2/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pmd() Message-ID: References: <20250613092702.1943533-1-david@redhat.com> <20250613092702.1943533-3-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250613092702.1943533-3-david@redhat.com> X-Rspamd-Action: no action X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C1A2114000D X-Stat-Signature: fzddos6at5qknfgtm66ro8h3mey4siwq X-Rspam-User: X-HE-Tag: 1749822600-634753 X-HE-Meta: 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 mPqPg0AK kseaPZ8vhf85iLLXw5osOUJhio+wVaHsq2Sq/1Yp7JbRyfMxquC74btqttgmKu9mwarZsP0qJp1bZ22A/3gWAd/zmi5209Lrh4gJ4ql/Uw0Eet9ifC/YpT2rEjvJoQ3Ff3+fl8EurBId9IDHtUpHEP11Zpk/SS+mM2vbGwGmdU69FNKimU+/lNZj0gJY0dZAmTk4DyAH4lxCNkQ4ZTjZdqHfzcMxWjJULlcZwmNlEi6/Pbm/m54szhlFSBmDvwRwtmsx22UlVLoZO8/9vx1OAGEG73+K5Ku9tY8ykAcjrac5oyPxG8LYGhVrMdo8Yr+lZY+kMrzPjDS+SqzrS8qI9sFXLBv+jP/vPyrIRgJUcOTVSXgllnHOFf7Z7Mt5ctZvc705/JBDR3gpnoHZgRcYEa7TvTQ== 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: List-Subscribe: List-Unsubscribe: On Fri, Jun 13, 2025 at 11:27:01AM +0200, David Hildenbrand wrote: > Marking PMDs 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 pmd_special() check that can be > mislead, and most vm_normal_page_pmd()/vm_normal_folio_pmd() users that > would get this wrong right now are 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 use > folio_normal_page_pmd() in more places. > > Fix it by teaching insert_pfn_pmd() to properly handle folios and > pfns -- moving refcount/mapcount/etc handling in there, renaming it to > insert_pmd(), and distinguishing between both cases using a new simple > "struct folio_or_pfn" structure. > > Use folio_mk_pmd() to create a pmd for a folio cleanly. > > Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()") > Reviewed-by: Jason Gunthorpe > Reviewed-by: Lorenzo Stoakes > Reviewed-by: Dan Williams > Tested-by: Dan Williams > Signed-off-by: David Hildenbrand Altough we have it quite well explained here in the changelog, maybe having a little comment in insert_pmd() noting why pmds mapping normal folios cannot be marked special would be nice. But just saying :-) Reviewed-by: Oscar salvador -- Oscar Salvador SUSE Labs