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b=U7lhpOz2V9rjd0zWT8krD+LZt3v1GQPuKmCukHl/7x7wY9DvYezxlkpiTF8vcsjzF ha+2mMxkmKc7BvRPbSCjlCdQbgwj7ZmXXeflh2but+bff51Dj1LQA0rf6z48ad6qbH uu0tjJ8c+sXQ95Pv62HTCo70d9TlC3u0c9+SFFtviD5Kgiq0xou+dXp91DZxVAdWUo 1ZaO0OfzoMtupVa40r9H/TLiR+e/uOG67SzaGkO91E1zQUDXs6K+tgrlUu9rvowIgE DXFVdukK+HWqV6vIvLiJ5nG/v3xnPjwHC5uTyn3k34tjomvJu4F7j7OvDGmhg5goqD OBphIxoXc5pnw== Date: Tue, 18 Aug 2026 00:35:15 +0000 From: Yosry Ahmed To: Brendan Jackman Cc: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , 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, "Kalyazin, Nikita" , patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Sean Christopherson Subject: Re: [PATCH v3 13/26] mm: introduce freetype_t Message-ID: References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-13-6f5729aa9832@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 658DC40004 X-Stat-Signature: bu6i8t8yyko8owhytzjkexeqgs1f3nu4 X-Rspam-User: X-HE-Tag: 1787013318-251161 X-HE-Meta: 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 WowfKmyV oH1uLU6POVoeYLhvPBrvtfnapBdXA0n4zudalHdxoLMRv26I/bhP/MJqcFrIwa/SMjncQ1bITpCm5iuVhnfv+jiIYEs/J8SX2oiDgWHi2MmYnkQhXxCDheotoGmWrrlVH58atFpQWpe2poxpacvGVLbBtpzowVqXH3PyCxWohjP77m756QrnA8UiL524kyqTQGgBX39rsokHQJ6wwNeoCSS32MIvT7y0hbMni3CttoUvRfXBNV7kwjxPLtC4f5XQLYPm3QXyGM7ThvNRivYTWOefEYKXpaWOPwspKRq3B6bHlgruCkFz+SXO8fPP+uXeSGiBg Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > >> +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.