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[67.164.59.41]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b4cd38610edsm14886181a12.54.2025.09.03.11.19.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Sep 2025 11:19:11 -0700 (PDT) Date: Wed, 3 Sep 2025 11:19:09 -0700 From: "Vishal Moola (Oracle)" To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] mm: tag kernel stack pages Message-ID: References: <20250820202029.1909925-1-vishal.moola@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: E7E3E180011 X-Rspam-User: X-Stat-Signature: iohbkwndjsks3w996ubm1xx5akhykxr9 X-Rspamd-Server: rspam09 X-HE-Tag: 1756923553-290494 X-HE-Meta: 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 RK/6eG3O 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 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 Wed, Sep 03, 2025 at 09:49:06AM +0200, David Hildenbrand wrote: > [resending my original mail because it might have landed in the spam folder] Ah, indeed the original mail was found in my spam folder. Thanks for resending. > On 20.08.25 22:20, Vishal Moola (Oracle) wrote: > > Currently, we have no way to distinguish a kernel stack page from an > > unidentified page. Being able to track this information can be > > beneficial for optimizing kernel memory usage (i.e. analyzing > > fragmentation, location etc.). Knowing a page is being used for a kernel > > stack gives us more insight about pages that are certainly immovable and > > important to kernel functionality. > > It's a very niche use case. Anything that's not clearly a folio or a > special movable_ops page is certainly immovable. So we can identify > pretty reliable what's movable and what's not. > > Happy to learn how you would want to use that knowledge to reduce > fragmentation. 🙂 > > So this reads a bit hand-wavy. My thoughts align with Matthew's response. If we decide "This doesn't add enough value to merge it upstream" thats fine by me. Otherwise if we think this is useful, I can respin this with your suggestion below. > But I wonder, if this should actually go to the actual place where we > alloc/free. > > Now that it's no longer required to clear page types when freeing, > alloc_thread_stack_node() might be a better place to set it, and to > leave it set until freed. I think this would be a better place to implement it as well. > I'll leave Willy whether we actually want this type, cannot spot it > under [1], but if we have sufficient types available, why not. > > BUT > > staring at [1], we allocate from vmalloc, so I would assume that these > will be vmalloc-typed pages in the future and we cannot change the type > later. > > > [1] https://kernelnewbies.org/MatthewWilcox/Memdescs > > > -- > Cheers > > David / dhildenb >