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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-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 93E111A0006 X-Spam-Status: No, score=-10.8 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: 9yh4msfhe3r8rhnsxkgudr375gjdqpxd X-HE-Tag: 1792679136-646525 X-HE-Meta: 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 6pCj81X7 VfSpAr8rl6jsnq+OQ/0rMkFk7j9PJJzE6+i10s40U+hyh/F5LdJFvXOhZk4yNoPbHuqSM6BnpBx7uF51qiD2v0oJudW6WP+AztYT+1sblMrbMlqFYE6X7ndLANWCHyLXqa8nDKcBPRwqZuHlMi1D0GyPpcYGWwW/+Ku/qqii5GpiEwL3f6kqOcXexLpHcDI/TDUTC/vpAcTH/IRMSs80hjOjEyRDBsWY0gC2eq9aPux3lLW2BVe1+MKbKnzRCgi921r6KZJby9xBqfLpzEjbyQ4BNpzqiun+BywvacZjcQpJgg1R9J0bkMDJcZdyM4MS6UK+BOvnzNDkzfmkqXtMx9H4IjYF4NfJmAigr3/BfppfYkdpwER0LU35kiYY+8z9KVO9FWDqEqLJaDR+YdPq/L7BueLzLQ494rZGAEbnf4no2HVzkYNuBYFp85ipG2ixXR29ttKGWqhBzCV5eNwQrIw5aBbUXgdQ/tMlgC6Cu3iUoVWli2Y1Kb7AdfYYI5CQgc2TxytFCEvwIVb4= 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, 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