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Thu, 22 Oct 2026 07:25:34 -0700 (PDT) Received: from localhost ([2a09:bac6:37a8:294b::41d:9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e258213cesm12905886f8f.11.2026.10.22.07.25.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 07:25:33 -0700 (PDT) Date: Thu, 22 Oct 2026 15:25:31 +0100 From: Matt Fleming To: Marco Elver Cc: Caleb Kan , 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 03/11] mm/page_owner: preserve accounting with countable stack depot records Message-ID: References: <20260908-stackdepot-trie-v2-0-1996d5cef732@cloudflare.com> <20260908-stackdepot-trie-v2-3-1996d5cef732@cloudflare.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Oct 20, 2026 at 11:11:24AM +0000, 'Marco Elver' via kernel-team wrote: > On Tue, Sep 08, 2026 at 02:13PM +0100, Caleb Kan wrote: > > > > @@ -609,6 +611,9 @@ static inline struct stack_record *find_stack(struct list_head *bucket, > > list_for_each_entry_rcu(stack, bucket, hash_list) { > > if (stack->hash != hash || stack->size != size) > > continue; > > + /* Page owner countable records have a distinct count lifetime. */ > > + if ((stack->flags ^ flags) & STACK_DEPOT_FLAG_COUNTABLE) > > + continue; > > This splits hash deduplication unconditionally even when > stackdepot.trie_enabled=0 (the default), and even for page_owner's > free_handle traces (__reset_page_owner()), which never touch > stack_record->count. Prior to this patch, persistent hash records had > refcount_set(&stack->count, REFCOUNT_SATURATED) and page_owner safely > overwrote it with its 1-biased page count while still sharing records > with non-GET callers. > > The interface looks error-prone to me. OK, fair point. I think the best course is just to make the trie backend work with the ->count mechanism too so this whole problem goes away. Thanks, Matt