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[35.205.100.124]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1f2d1e8ebsm73417245e9.3.2026.10.20.08.07.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 08:07:44 -0700 (PDT) Date: Tue, 20 Oct 2026 15:07:40 +0000 From: Marco Elver To: 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> X-Archived-By: 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> User-Agent: Mutt/2.3.2 (2026-04-26) X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B4FE81A0011 X-Stat-Signature: hw7sfwqjrmafxxq16zbpz8tmmcyf78ua X-Rspam-User: X-Spam-Status: No, score=-14.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=4.0.1 X-HE-Tag: 1792508867-44989 X-HE-Meta: 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 t+CZwJRa irfnNI2WpY46/eiuFkNJv9cuaZVTgsQWAc+tLYhJZxRNJUpk4F3V6jO0rMGHTey8rE4xT/AaXrd9B/wtGY6zk/6fE2L9QVpyQAtWB59OSmoy3N49zyH73thXpfR3UCHFEKDV7IC1hiK63jy2BjOfqzCZJAt7EtKTEKfDD54tIohdGMHYxI4v3Qtjq7JRCUMelASTFlUIcABAzaK9e2Uh24mB29aLm6ls0eL8dL1w8BqtC1uMiOq0H0QVkNaZcobbAdmR52TxOL+/DEex5FNUXfnegW3OHn5u6ximtD1kVwSIfZmU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Sep 08, 2026 at 02:13PM +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. Have you measured how much of the memory reduction comes simply from storing 32-bit compressed frames (patch 9) directly inside the existing hash-backed struct stack_record? That alone cuts frame storage by ~40-45% across *all* callers (including page_owner and KASAN aux stacks) with O(1) lookups and none of the trie/bitmap/RCU complexity. If prefix sharing is still needed on top of that, deduplicating fixed-size (e.g. 4- or 8-frame) immutable segments from caller to callee in the existing hash table (chained via parent_handle) would avoid mutable child arrays, RCU retirement, and the bitmap allocator entirely.