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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=GUmn4JfB0jh0NLkd/QxuENHfGYYuCh4n25zdfDVPY0Ej30DIrxWLwvOm0/eySV8Kf pDQ5QEBRaNUX8aDLq4hX/UCYJciU8PSbEOmcJRk8tR/aA316X5X8xG9X66sz4fb0zF KaFk4h0OpI6u8PnOeMcq20BAXqsc7d92Dw2b8cgw= Message-ID: Date: Fri, 24 Jul 2026 10:35:34 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/5] mm/rmap: convert page -> folio for hwpoison checks To: "Lorenzo Stoakes (ARM)" 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 References: <20260710055915.638659-1-dev.jain@arm.com> <20260710055915.638659-2-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: sgxgbsogikuyr3nomsecg9cam4x8soz3 X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 58C08140007 X-HE-Tag: 1784869546-334574 X-HE-Meta: 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 qvngReVz ssWT8VtNHylg3/9I1GOad4r5bEb+0OPq0psiS5OESSMNBLEbtDkWyhXZObfSSrxIM7x+KzyjjlKPVRQRO6Sib1qxPL1QkxtixBz8RqJzNegc3haP1o1/l4SQcuWpbS5xDMxSKS2R1QqVFF+HZr06yky31+hlVEiil9xp/QqjTPyUs1XCbpDh/41kyQJ+hphf/RHyeob6Vp+nXqhQxkD7AaAklJ74DF5sw8wCD+f/rtQ2D0yKbj8voGt/mhGs27HVDt3MZaxw41Z4vmVvYy1x3IuPZ+Ih1ZBT7fZ2QubHMz9jVrozt1AFVzEhjDKxZES5sCY5V Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 23/07/26 10:45 pm, Lorenzo Stoakes (ARM) wrote: > 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? :) I had posted a v3 here: https://lore.kernel.org/all/20260713050050.1017741-1-dev.jain@arm.com/ In that I had fixed this comment to drop "or hugetlb folios ..." . But I would still like to retain the "only expect small folios" comment, it adds cognitive load when I am reading try_to_unmap_one and then have to go read hwpoison code to figure that large folios would be split before coming here. > >> + 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