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b=a91Ja4pkPFklSAR319qDqsm3kB/UTDdEb6q6mXYT2v0zJDeC8m0klOVfMIVWdYKsB /Odo9jiAysHptRQg9KgDpdWt6UgCsAL9P3iXgJaTD4VtpTXTFSLbBjvbU4aUlQQTTC tAse9zBNc+cNyYdP3BjIcyBboBU7D8G5KdudWDETco7pCQCp8sIYAgQ8t/05Pq7bwK jR5p9TXRn8mRxz40fSLv+P4/irIfW8AFpMBDOJd00rRPMzOGo88nWYms5GyBk117FJ uJyTZpYftzt3zIB4n+XALKGwsBalzzduTdZNIM+G7/7BYIEpGQcx1JWKJgmsgmPqC4 PG3Lerzt5KkCg== Date: Thu, 23 Jul 2026 18:15:50 +0100 From: "Lorenzo Stoakes (ARM)" To: Dev Jain Cc: akpm@linux-foundation.org, david@kernel.org, muchun.song@linux.dev, osalvador@suse.de, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: Re: [PATCH v2 1/5] mm/rmap: convert page -> folio for hwpoison checks Message-ID: References: <20260710055915.638659-1-dev.jain@arm.com> <20260710055915.638659-2-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260710055915.638659-2-dev.jain@arm.com> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A7E2DC0007 X-Stat-Signature: mznnayeoqroo8jyyoa67suufqn8sc7im X-HE-Tag: 1784826970-80399 X-HE-Meta: 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 xeMpLkVD aOUJ4kmrlVdn4BFp6YJQbtigCTgVUshqSGto9Zkm3PhotoT3vu7ov3ZWpe+LUf1QJxUNHEVdlLcso6TYay44wuJzZWNTQIxQMlBp2nY+JvaDrv9bB6C2mvQfnjUoUOhW8uuzHeecLAKxRtsUP4cReyyJf7vP5ilZFly6/3LnMHikXnZFpezEH7JOBkg1V/Puqm5zxdpCjNe4dTxyZLFe1DODqNZARw0kRGpOY1OJ5qdRtlAppWTMK0q1mTQxNexuuLEY3PhOnXzFuizER76+AG4wqkKf58edkcxLH53jW2/1g7RZ1AHRbuTBoXkw9LhdxounT10Wzx8mvT38CqEUH2CzsmA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jul 10, 2026 at 05:59:10AM +0000, Dev Jain wrote: > try_to_unmap() receives hugetlb folios only from the hwpoison path. Horrifying :) > hugetlb_update_hwpoison() sets the hugetlb folio's head-page > hwpoison bit, and page_vma_mapped_walk() reports the hugetlb mapping at > the head PFN, so the previous PageHWPoison(subpage) check happened to > work for hugetlb. > > For non-hugetlb folios, unmap_poisoned_folio() currently rejects large > folios before calling try_to_unmap(). Hence it is always the case that > if try_to_unmap_one() handles an hwpoisoned folio, then the head page is > marked with the poison bit. > > Therefore, convert the poisoned subpage checks to folio_test_hwpoison(). > > No functional change intended, except that, while at it, > convert VM_BUG_* to VM_WARN_*. > > Acked-by: David Hildenbrand (Arm) > Signed-off-by: Dev Jain Small nit below but generally LGTM so: Reviewed-by: Lorenzo Stoakes (ARM) > --- > mm/rmap.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 9939400e77c79..dbb077f8443e3 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2122,10 +2122,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > bool anon = folio_test_anon(folio); > > /* > - * The try_to_unmap() is only passed a hugetlb page > - * in the case where the hugetlb page is poisoned. > + * The try_to_unmap() is only passed a hugetlb folio > + * in the case where the hugetlb folio contains a > + * poisoned page. > */ > - VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage); > + VM_WARN_ON_FOLIO(!folio_test_hwpoison(folio), folio); > /* > * huge_pmd_unshare may unmap an entire PMD page. > * There is no way of knowing exactly which PMDs may > @@ -2204,7 +2205,11 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > /* Update high watermark before we lower rss */ > update_hiwater_rss(mm); > > - if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) { > + /* > + * With TTU_HWPOISON, we only expect small folios or hugetlb > + * folios here for now. > + */ I think probably we can drop this? It seems implied by the code (David comment similarly I think? :) > + if (folio_test_hwpoison(folio) && (flags & TTU_HWPOISON)) { > pteval = swp_entry_to_pte(make_hwpoison_entry(subpage)); > if (folio_test_hugetlb(folio)) { > hugetlb_count_sub(folio_nr_pages(folio), mm); > -- > 2.43.0 > Cheers, Lorenzo