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Message-ID: <bd36e972-8900-4476-a66b-4dc218b21a4d@kernel.org>
Date: Fri, 15 May 2026 17:29:01 +0200
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Subject: Re: [PATCH 4/4] mm/page_alloc: remove ifdefs from pindex helpers
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To: Brendan Jackman <jackmanb@google.com>,
 Andrew Morton <akpm@linux-foundation.org>, Kairui Song <kasong@tencent.com>,
 Qi Zheng <qi.zheng@linux.dev>, Shakeel Butt <shakeel.butt@linux.dev>,
 Barry Song <baohua@kernel.org>, Axel Rasmussen <axelrasmussen@google.com>,
 Yuanchu Xie <yuanchu@google.com>, Wei Xu <weixugc@google.com>,
 David Hildenbrand <david@kernel.org>, Lorenzo Stoakes <ljs@kernel.org>,
 "Liam R. Howlett" <liam@infradead.org>, Mike Rapoport <rppt@kernel.org>,
 Suren Baghdasaryan <surenb@google.com>, Michal Hocko <mhocko@suse.com>,
 "Rafael J. Wysocki" <rafael@kernel.org>, Pavel Machek <pavel@kernel.org>,
 Len Brown <lenb@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>,
 Zi Yan <ziy@nvidia.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
References: <20260513-page_alloc-unmapped-prep-v1-0-dacdf5402be8@google.com>
 <20260513-page_alloc-unmapped-prep-v1-4-dacdf5402be8@google.com>
 <4074a816-9e75-45a6-8141-25459bcc106b@kernel.org>
 <DIJA0MM2F3D2.61WBO3MJZRNQ@google.com>
From: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
In-Reply-To: <DIJA0MM2F3D2.61WBO3MJZRNQ@google.com>
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On 5/15/26 15:15, Brendan Jackman wrote:
> On Wed May 13, 2026 at 5:19 PM UTC, Vlastimil Babka (SUSE) wrote:
>> On 5/13/26 14:35, Brendan Jackman wrote:
>>
>> Uh yeah, VM_BUG_ONs are frowned upon now. But doing a VM_WARN_ON_ONCE here
>> makes little sense. There's no safe fallback if we end up here with a wrong
>> value. 
> 
> Isn't that grounds for upgrading them to a real BUG then? My experience

If Linus noticed, there would be yelling :)

> has been (I broke this code lots of times lol, I REALLY struggle with
> this arithmetic stuff) if something goes wrong here the machine quickly
> gets irrevocably and undebuggably borked. Crashing is the best case
> scenario.

Yeah it will crash quickly anyway if you mess it up. I guess if the check
would help you find more quickly what you messed up, a VM_WARN_ON_ONCE would
still have some value even if it can't avoid the imminent disaster. So maybe
just switch it to that.

>> And it's all internal to page alloc so I'd just drop those checks
>> completely at this point.
> 
> But, I won't die on the above hill, if people really hate BUG that much
> happy to go with the flow. 
> 
> In that case, I'd suggest we drop them as a separate patch.