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b=d7iRT08pKtrpl+FS8F9XGYWGb54fjKRbJt/wm7yMpEXiokgdrv23tgEn8Dje5lFxB Xpel97egrz56kjU20xZ4pk4d0TtaQ+G+af792PD36Zccz2MkZQ/aMYkK85gA3YsjAD BGRwxxvOg7bPL2QDe7W6+cmgR2QlNoOo1+y7Y32T1P4YxFCmmjVSh+Osfiu3ya0Vl3 cjLDlkcxY70ZVR01S80kC9kcUhQt9eQobn7vu5qjlq3+4kGVEXa+xf8vBHOSGTMJfu BaOO4k16B0EpfQpyBMrlzKbuzQYoQ1cUGKB4mtlyZNUKNNbue7QcTW9+WydcfQpqe7 hgEgZEcEaUr2g== Message-ID: <76dd87e0-cd34-4ce2-9586-d7ff019b1fb9@kernel.org> Date: Thu, 3 Sep 2026 10:00:22 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 13/26] mm: introduce freetype_t To: Yosry Ahmed , Brendan Jackman Cc: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Mike Rapoport , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sumit Garg , Will Deacon , rientjes@google.com, patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Sean Christopherson References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-13-6f5729aa9832@google.com> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: EB1EB12000F X-Stat-Signature: rj7ww3brt4rn9p6eg5bdwp68ynbt8z6h X-HE-Tag: 1788422429-447502 X-HE-Meta: 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 CB7G/WkJ K1L4GT47ZxOJvjesGidW1eCZcOS6LSfrfEh9ITTLYsQAPDiHfJ7iaPh1rbXylM1VUmD0lso5ArpmF+rIPGF6Mp0MwynrikYoZbBqEK79122xKC42ANSgCqELnQbtnuE+0R05+i5Uk0UmWDCktPA4JfQtp0XVDHeJeNer3g3mKsZR0Ps/i6T3n38SvNes1JNHOX4QHFWU3sEFv03PjXxE6m/ATD0JBpygcxNLs0aXYRDAomj5ZZbozApFs+RwQugbzb+UupqOFR29/r/mfnn6iP0qm8NKn82GYF4rIlqUGQEg63xbcW686g3aRwYwrGFO7sCtVzQh1P9AimKI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/18/26 02:35, Yosry Ahmed wrote: >> >> +static inline >> >> +struct list_head *free_area_list(struct free_area *area, freetype_t type) >> >> +{ >> >> + int idx = freetype_idx(type); >> >> + >> >> + VM_WARN_ON(idx < 0); >> >> + return &area->free_list[idx]; >> > >> > Should we return NULL here if idx < 0 instead of an out of bounds >> > access? >> >> TBH my descending order of preference is: >> >> 1. >> >> BUG_ON(idx < 0); >> return &area->free_list[idx]; >> >> 2. >> >> if (WARN_ON(idx < 0)) // OR VM_WARN_ON >> return NULL; >> return &area->free_list[idx]; >> >> 3. >> >> VM_WARN_ON(idx < 0); >> return &area->free_list[idx]; >> >> 4. >> >> return &area->free_list[idx]; >> >> But I suspect[0] Vlastimil (and Linus) would order it the exact opposite >> way. >> >> [0]: https://lore.kernel.org/all/bd36e972-8900-4476-a66b-4dc218b21a4d@kernel.org/ >> >> And I care more about making Vlastimil (and Linus) happy than this tiny >> detail of the code, so I'll defer to him. The current style is a >> compromise, but maybe it's just a compromise that makes nobody happy. > > I think I prefer #2 (regardless of whether it's WARN_ON() or > VM_WARN_ON()), let's see if anyone disagrees. #2 can't work with VM_WARN_ON as it returns void. Otherwise if it evaluated the cond with DEBUG_VM and hardcoded false otherwise, it would be ideal. I don't remember why it's not. Do the callers all handle NULL safely? In that case #2 has some merit (maybe with WARN_ON_ONCE()) otherwise #3