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[109.81.91.107]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-451f8f13375sm35020835e9.1.2025.06.06.03.13.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Jun 2025 03:13:28 -0700 (PDT) Date: Fri, 6 Jun 2025 12:13:27 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Jason Gunthorpe , John Hubbard , Peter Xu Subject: Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs Message-ID: References: <20250604140544.688711-1-david@redhat.com> <1a65d0e6-6088-4a15-9c19-537203fe655c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 96057A000C X-Rspamd-Server: rspam09 X-Stat-Signature: 5mimkqdjgjmaom5z6thp33p4c5wjwby8 X-HE-Tag: 1749204810-575696 X-HE-Meta: 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 3CTPDlSt Xexh6qS/N/NRGhqm6Us+6k6a9UY6t6yEgdC/WNfHxdLcuXATbnOCd6Ja9tiNF80MvTywWq1uWr0rGdDsCLw4aRegLY3CW2ZHVjHSYkulrkxZIYQYC/qFSKVdEgs8CsqUJRi2jhtoDPr/cYT5CELrHN7RLQQocxBbbBsTLcL1ktW4o2Ow1iW1OSZpGoFjIazXXxQO668RgR73GaySduYTWlybKZUMsQYWuroPgD72dq0+ijNPfM/MoZQnhefcCq23lW1QEjg8IjOb7iePJAUgcJK8Q07qUuLMsBRb81w0G3AhmegYmWZdqm3HkAWfD5WsUMkrr5Ce32/72XHCzlRlbhFqWCVCYWT8XhAMccuTk94ejbe4= 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 Fri 06-06-25 11:01:18, David Hildenbrand wrote: > On 06.06.25 10:31, Michal Hocko wrote: [...] > > Turning them into VM_WARN_ON > > should be reasonably safe as they are not enabled in production > > environment anyway so we cannot really rely on those. Having them in > > WARN form would be still useful for debugging and those that really need > > a crash dump while debugging can achieve the same result. > > One question is if we should be VM_WARN_ON vs. VM_WARN_ON_ONCE ... *WARN_ONCE ha a very limited use from code paths which are generally shared by many callers. You just see one and then nothing. Some time ago we have discussed an option to have _ONCE per call trace but I haven't see any follow up. Anyway starting without _ONCE seems like safer option because we are not losing potentially useful debugging information. Afterall this is debugging only thing. But no strong position on my side. > VM_BUG_ON is essentially a "once" thing so far, but then, we don't continue > ... so probably most should be _ONCE. > > > > > So while I agree that many of them could be dropped or made more clear > > those could be dealt with after a mass move. An advantage of this would > > be that we can drop VM_BUG_ON* and stop new instances from being added. > > As a first step we could probably just #define them to go to the > VM_WARN_ON_* variants and see what happens. You meand VM_BUG_ON expand to VM_WARN_ON by default? -- Michal Hocko SUSE Labs