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[2003:d8:2f37:2b00:948c:dd9f:29c8:73f4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b93fae643sm5496885e9.3.2025.09.01.08.35.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Sep 2025 08:35:51 -0700 (PDT) Message-ID: <3b30e9fd-4035-42f2-a7ca-3a670bb79dd5@redhat.com> Date: Mon, 1 Sep 2025 17:35:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: Enable khugepaged to operate on non-writable VMAs To: Dev Jain , akpm@linux-foundation.org, kas@kernel.org, willy@infradead.org, hughd@google.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250901074817.73012-1-dev.jain@arm.com> <620f01b4-8a6c-4dac-bcdd-7c48f5cd87f2@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 01.09.25 17:26, Dev Jain wrote: > > On 01/09/25 2:02 pm, David Hildenbrand wrote: >> On 01.09.25 09:48, Dev Jain wrote: >>> >>> @@ -19,7 +19,7 @@ >>>       EM( SCAN_PTE_NON_PRESENT,    "pte_non_present")        \ >>>       EM( SCAN_PTE_UFFD_WP,        "pte_uffd_wp")            \ >>>       EM( SCAN_PTE_MAPPED_HUGEPAGE, "pte_mapped_hugepage")        \ >>> -    EM( SCAN_PAGE_RO,        "no_writable_page")        \ >>> +    EM( SCAN_PAGE_RO,        "no_writable_page") /* deprecated */    \ >>>       EM( SCAN_LACK_REFERENCED_PAGE, "lack_referenced_page")        \ >>>       EM( SCAN_PAGE_NULL,        "page_null")            \ >>>       EM( SCAN_SCAN_ABORT,        "scan_aborted")            \ >>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c >>> index 4ec324a4c1fe..5ef8482597a9 100644 >>> --- a/mm/khugepaged.c >>> +++ b/mm/khugepaged.c >>> @@ -39,7 +39,7 @@ enum scan_result { >>>       SCAN_PTE_NON_PRESENT, >>>       SCAN_PTE_UFFD_WP, >>>       SCAN_PTE_MAPPED_HUGEPAGE, >>> -    SCAN_PAGE_RO, >>> +    SCAN_PAGE_RO,    /* deprecated */ >> >> Why can't we remove that completely. > > (I raised this query in the other mail but due to not snipping stuff in > between, > I saw it but forgot to reply :) > it may have been glossed over) > > I was wondering whether a userspace script could break which assumes > scan_page_ro > > metric is there? I played with tracing long time back so I don't remember. If it's part of a stable abi/api, then it could be a problem indeed. I don't think trace events are in general not stable abi/api. In practice I think some are (e.g., in scheduler). I assume we can safely drop it, just like we can add new stuff. After all, if "SCAN_PAGE_RO" never happens anymore, we would never be running into the __print_symbolic() with that value. -- Cheers David / dhildenb