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Fri, 24 Apr 2026 14:35:21 -0700 (PDT) Date: Fri, 24 Apr 2026 21:35:20 +0000 From: Pasha Tatashin To: Dave Hansen Cc: David Stevens , Pasha Tatashin , Linus Walleij , Will Deacon , Quentin Perret , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 00/13] Dynamic Kernel Stacks Message-ID: References: <20260424191456.2679717-1-stevensd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: t6g7cc9yyihp888bcemksxmwy3aoxr9j X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 31FB840005 X-Rspam-User: X-HE-Tag: 1777066523-153230 X-HE-Meta: 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 6yNsRlDO mGKVpdr0lrUkd/HBIXgp+v260db5P2V/N/I5P4SskCyGNQqMRsBtx1dFGq/qoODVIMdZKRZnDIUbF7IbGOHnanSLxHyGLqMD7sdi9E5GE5Xq0EJ24mNnZuqiRcuMa5sO6jpaJSfTlHnNu8wyK8u3MRFLOcIWq8ZLvbIu5xLkCsqU44ynzGSZEYPdi4dm+ylfzOUqWrJYgfWYvTaAWAfxjgl+ChUWgulues+IaQQgQbUmrKPdjgpawH5tYFis0MV4siHpPkStYfGD6M2Lvrksj9nIMV/wCBYF7lv6ovyOf4bHp6AO0o6PrKY7CnQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 04-24 12:41, Dave Hansen wrote: > On 4/24/26 12:14, David Stevens wrote: > > The question is then: is this approach something that is fundamentally > > untenable in the kernel > > Yes. Fundamentally untenable. > > Not allowing stack faults has been a wonderful simplification. It's one > of those things that just plain makes the kernel easier to maintain. > Saving low single digits of system memory is not exactly making me eager > to go back to the harder-to-maintain days. > > I seriously doubt that this 1% is the lowest hanging fruit for memory > bloat on these systems. ;) This true until, in a fleet of millions of machines, you encounter a one-in-a-billion chance of a stack overflow. You are then forced to double the statically allocated kernel stacks on every machine, paying a memory tax even though 99.999..% of threads never exceed 4K. This overhead accumulates to petabytes of wasted capacity. Pasha