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Wed, 07 Oct 2026 03:34:05 -0700 (PDT) Date: Wed, 7 Oct 2026 11:34:04 +0100 From: Matt Fleming To: Marco Elver , Caleb Kan Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Vlastimil Babka , Alexander Potapenko , Dmitry Vyukov , Andrey Konovalov , Oscar Salvador , Caleb Kan , kernel-team@cloudflare.com Subject: Re: [PATCH RFC v2 00/11] stackdepot: reduce memory use for persistent stack records with a trie Message-ID: References: <20260908-stackdepot-trie-v2-0-1996d5cef732@cloudflare.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260908-stackdepot-trie-v2-0-1996d5cef732@cloudflare.com> X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 4550C1C0009 X-Stat-Signature: o8gkdn33gz75fah4ontxgt3qs4hq7g9c X-HE-Tag: 1791369247-604884 X-HE-Meta: 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 t3SKp8rC 5CQSQKn48pA+WAlRBfhAjSltHWWu2VCu+K1P6qLdnOjsjFHz3JNFgxSxQYS2ApWki7SKzXwf0czw1e91jsAkI3hiQYbHmySPM5vwbGGb1yaeuIlxTEWIyqTBHbAZs0VFxORzJWyfcEQrgHYcP1826ppudFDvjUMK9VxYuC6lZuKe+JFtTguOSyqGbRDs5pBmI0iDLvI3L5EheWI9gblyahLNSQBirLLfHv6d9NGDO5wHD65kgTNHyimVz5/yhn74wrTLPxok8q6otIOlbUJSsfrrwwauzpNJipZhW122LN8mb9CjokFi3QVTLytN6GfgSJyIfv1fwuib8phBiCQUK4nVfEalYpAw+9y9czuUuE4kjEUsDa7e2KdNX48UfEQhDtsYzgLprLk+J5N8pT73/Pe7JfPbSdLhgGxMI4CzWt5YQDsEyMw0w3k8xNay/WjXpfJVYhgAb0f03dOe8lUY4jypc+w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 08, 2026 at 02:13:33PM +0100, Caleb Kan wrote: > Hi, > > This series reduces the memory used by persistent stack depot records by > sharing common frame prefixes in a path-compressed trie. > > Cloudflare runs KASAN on pre-production servers so allocation and free > stack traces are available when diagnosing memory-safety bugs. On some of > these servers, stack depot exhausted its pool budget even after we raised > stack_depot_max_pools from 8,192 to 32,768. Once the depot is full, a new > persistent trace returns no handle and a later KASAN report can lose the > history needed to explain the bug. > > With 4 KiB pages, 32,768 order-2 pools allow 512 MiB of stack storage. > Doubling the limit again would allow 1 GiB, but it would not change the > linear growth: the hash backend shares identical complete traces, while > two traces that differ by one frame are still stored independently. > > The trie is opt-in and disabled by default. Hey Marco, Do you have any more feedback on this series? Particularly the bug fix in patch 1? Thanks, Matt