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b=VyR0idXeoumMGEz4qF3gxKOoFnSwT/pbENQpscBE5SRoF2O2w8SF1wHSFlGrrpELe t4cKLJy2E4itK/es8Pe8vaRir4xgRSEv/dbGYgPKPPi+IGCnwpy5U5ESzjm1k0NFWE 9Gz6WUXtdOMzXd+hOZFmTfyzwVeDK8Q7FpY6ckcHuoFvsxC8MhadVMFewnBoZBFyO3 0y5Qvt7gou1b1IIkqikJZx5SIe3eCWKQw2YNOYgk2F5Ww7OOO8kN+FDb6t6z1Hxryh 75i5MW0esmKBEkw6BKqn2H51xYX2cfuHvPm4ZjYwHBkMBtNcP1YLpg9yedEFSQ37ej Aq1RXfS57ExFw== Message-ID: Date: Tue, 9 Jun 2026 15:44:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 01/12] mm/rmap: convert page -> folio for hwpoison checks To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org, chrisl@kernel.org, kasong@tencent.com, hughd@google.com, liam@infradead.org Cc: riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, baolin.wang@linux.alibaba.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260526063635.61721-1-dev.jain@arm.com> <20260526063635.61721-2-dev.jain@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: BF8FCC0015 X-Stat-Signature: d191wyz7q8jobxo1edjm77mewukfjf3q X-HE-Tag: 1781012708-858401 X-HE-Meta: U2FsdGVkX18I9uEAZnR9Iuq6BQAy5dsE8a2X0Yq/GD36GyeYEFkkfMjOsLyTuq5uiAl0zE0iuzofPD/YsxDkxMrHHty2iwA/JoGv4nGAuPGEETccO02myoDouAANAxXrqcYiiAaiXaPeOJMYMFfaYADhuQI2LueO9LfVljF7OwDwYHLaFc8hDWrtkVmAh48qgnHhtUHXA2/344+WvtBcWzbzWvBN6yAI7R36z2D3gAU0r3yXLKODGIvLaeK0XdoW5q0kZvLiRebYy+S6tgBWL0gCAwISgBH0FPlEu5KrEWA2BxKMVs6TEpzO4DiIRa1CEVo0qxKVPTsVJtwMT+a6MeXDhVqtpxGdpC5Wwfj6fqki/KDs6zDShftgC+k7VdD78oiao5KipfpRe2FfrYQ07TEf/6VT5HfvhAfbEUykksLjSsOmDAIHgqfa06QGohRFmP6rZFyZUgBgbEUi4MtvpQpBZGrcAzsBaefxzJgvNobMA2q+EcyyuiMq9vu54Lflrqe2cLNep6/b0A+RFJe/ytBZRnST3XXbJ9qmD+OF9Wg6UsbjR8uqAsxXG0OFS8wloDo6mo/NK4YKcsO5ZO3txmXeiEjlnl1O2BjnWgKV/guD60G6N87ced2EfGfF4e77pmYCDuK2v42hKn/f7PvmILrdg+V/VdKgtlu2Dx5PLvGfkIbFHfD57Ho9GoOwXy3O6uo7lwYujq/YMarE0qTvhsJvVAyZ2g9tYcJhPqAt8GHY1V7U1cusrmvHexQXn+3OSMY/2ZsQW6I9REpqpSEHMvyg+otK1IC5wGnS/8l47o5rZZAC1HfM67ArTqcS4fvNOeC2ifKOXNe1CEkrNzVVit15CaQ8xKr+77dO5nCQkDNj7IenDvdNl1PG2SeN5LOO/XJsvpLKjluahAUZxZKgb6ckaewpbgDocbdw2b5aTpmKPzdgflcq0hcc4Abub8vym3rP/z8ed8Rx6UgZDmy yLTntN4i bDDuJHKxRDzLzp4hbhdXv3McEkLi6n7Q36p1hHw41AlUKENFC3OV58xkUYvOQ6XHSk+dc6EHLScfsONp9qmawU5z0Cf1cZsIJ7FWjr8/FdpUvuwiTEbCEXF4XN6nc3xS5mRGZKf+dlamay+Q9Yhpoj6VlIbPt+zGaEzTeDngnBLso4K2yhXal2kfi0KVQIeuVPbncokmJzlUqwOJu3pI+UMH0etXlossE6YrTCp37p2MrIYIrejzyNiNOGlGvaNUeSdiZPN6tbejsjkmtwiELt31oymguvHxvgUcmBiBxfkOaoU/+t6DMBRUUAejitc+UxWe9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/26/26 08:36, Dev Jain wrote: > If any page of a folio is poisoned, try_to_unmap() is called with the > intent to remove any mappings pointing to any part of the folio. > > Therefore, an hwpoison check on a single page does not make sense > (although everything works out because the memory-failure path sets > hwpoison on the head page too). Convert these checks to check whether > the folio has at least one hwpoisoned page. I think the reasoning is different and should better be described: 1) For hugetlb, we will always get subpage == head page (single PTE -> first PFN). try_memory_failure_hugetlb()->try_memory_failure_hugetlb()->hugetlb_update_hwpoison() will do the folio_test_set_hwpoison(). folio_test_set_hwpoison() is the same as setting it on the head page. For hugetlb, subpage==headpage That's why PageHWPoison(subpage) used to work. 2) try_to_unmap() cannot handle large folios (besides hugetlb folios). unmap_poisoned_folio() spells that out. That's why subpage==headpage right now. That's why PageHWPoison(subpage) used to work. > > While at it, convert VM_BUG_* to VM_WARN_*. > > Signed-off-by: Dev Jain > --- > mm/rmap.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index fb3c351f8c458..430c91c8fe2ae 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2116,10 +2116,11 @@ 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_contain_hwpoisoned_page(folio), folio); I think we could also just use folio_test_hwpoison() here. > /* > * huge_pmd_unshare may unmap an entire PMD page. > * There is no way of knowing exactly which PMDs may > @@ -2198,7 +2199,7 @@ 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)) { > + if (folio_contain_hwpoisoned_page(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); And here. Which might be cleaner, because folio_contain_hwpoisoned_page() is so far never called on hugetlb folios. Because folio_set_has_hwpoisoned() is only ever used on THPs, not hugetlb. It would currently work, but the expectation so far is that these primitives are for small folios+thp, not hugetlb. You could add a comment here, that with TTU_HWPOISON, we only ever expect small folios or hugetlb folios for now. -- Cheers, David