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 HwR6cZ3F Azfb3DJI5fpZzbg1siAw530B43QrHhIMygHkWX2HjkUVdzfZ9Yyc/+XqVe6UZwso2BefPXUfAlG4BQWrJOuF1TsUckH2TXIH5AijEOGhwseXR/mt7B/XA+ocGn5oAE8BhLpZbCWYSA4Q8SR/uBkMIG8THuNO7YXAxFJ+DBHiEWfRUyR7PPIxT1+QWBygETZ6X5TKdmgPiFnV/qFbPfHUGkfQFTGb0NUzqKhuwiUnEs+vGNDCdE4sJf8E3PtgzuTNxOKyQgbgvlavklVSoB4V5K6uRuPf8Iv/p3kfiObJqeQ/6f6+hpG9HyDLUAPUA8W8S0AXmRthqT4tqUp0kh1vtn2KF1s3KeLkKcmo2BbXL0s9b+hjw67Gpy35BnLpNpSd2AYDUzZFH5T6Mw2/yaVIfsIN5EKsAbpxNV8iwaZ0bDNYsWCY= 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 4 Oct 2025, at 22:35, Lance Yang wrote: > On 2025/10/4 21:11, Dev Jain wrote: >> >> On 04/10/25 3:12 pm, Wei Yang wrote: >>> On Fri, Oct 03, 2025 at 10:35:12PM +0530, Dev Jain wrote: >>>> On 02/10/25 1:02 pm, Lance Yang wrote: >>>>> From: Lance Yang >>>>> >>>>> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd() >>>>> and __collapse_huge_page_isolate() was almost duplicated. >>>>> >>>>> This patch cleans things up by moving all the common PTE checking logic >>>>> into a new shared helper, thp_collapse_check_pte(). >>>>> >>>>> Suggested-by: David Hildenbrand >>>>> Signed-off-by: Lance Yang >>>>> --- >>>> In hpage_collapse_scan_pmd(), we enter with mmap lock held, so for >>> This is true for the first loop, but we will unlock/lock mmap and revalidate >>> vma before isolation. >>> >>>> an anonymous vma, is it even possible to hit if (! folio_test_anon(folio))? >>>> In which case we can replace this with VM_BUG_ON_FOLIO and abstract away >>>> till the folio_maybe_mapped_shared() block? >>> But it looks still valid, since hugepage_vma_revalidate() will check the vma >>> is still anonymous vma after grab the mmap lock again. >>> >>> My concern is would VM_BUG_ON_FOLIO() be too heavy? How about warn on and >>> return? >> >> Frankly I do not have much opinion on the BUG_ON/WARN_ON debate since I haven't >> properly understood that, but this BUG_ON is under CONFIG_DEBUG_VM anways. But > > Yeah, VM_BUG_ON_FOLIO() is under CONFIG_DEBUG_VM, so it won't affect > production kernels. Many distros enable it by default. For mm, we are moving away from using BUG_ON or VM_BUG_ON. No need to crash the system if it is possible to handle it gracefully. > >> if you want to change this to WARN then you can do it at both places. > > It should flag such an impossible condition there during development. > So, I'd prefer to stick with VM_BUG_ON_FOLIO(). > > @Wei please let me know if you feel strongly otherwise :) -- Best Regards, Yan, Zi