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From: ilya.gladyshev@linux.dev Message-ID: <431c8a974d685d547b0ba1ebe887ce200291e044@linux.dev> TLS-Required: No Subject: Re: [PATCH v3 1/2] mm: drop page refcount zero state semantics To: "Kiryl Shutsemau" Cc: ivgorbunov@me.com, Liam.Howlett@oracle.com, akpm@linux-foundation.org, apopple@nvidia.com, artem.kuzin@huawei.com, baolin.wang@linux.alibaba.com, david@kernel.org, foxido@foxido.dev, harry.yoo@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, muchun.song@linux.dev, rppt@kernel.org, surenb@google.com, torvalds@linuxfoundation.org, vbabka@suse.cz, willy@infradead.org, yuzhao@google.com, ziy@nvidia.com, pfalcato@suse.de In-Reply-To: References: <5dabf3a748fee0c7b142c74367e7586f5db1ed1e@linux.dev> <7c28d766b007345f5f31ba9a086a3bffe95a013d@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7320A140011 X-Stat-Signature: f6wqrzhfsq9nqibwrcb1qecu1u935br5 X-Rspam-User: X-HE-Tag: 1780577287-842025 X-HE-Meta: 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 C3idwY51 1ASxL8OHTYUxUFMoTEMy7fGXewPMu2mZ4SauI+DEyK2ZhPD4dOCItgUZ5Y/uPftyPUM2j80ik6WpZ5XqBf4DkXO/eOf79fKrnKRjbFNUi5G+C4If0/ZTsrZhFR1hTOCBnAQU8uOUnoC7Ur7V7BgWZvdVaS7aKOqJfsuX2929FxEeZI6UsXrprT+D6QS9iTNhNnhtTW8xBxarHxN13RHY5mny9uw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >=20 >=20On Thu, Jun 04, 2026 at 10:15:12AM +0000, ilya.gladyshev@linux.dev wr= ote: >=20 >=20>=20 >=20> @@ -115,8 +120,14 @@ static inline void init_page_count(struct page= *page) > > set_page_count(page, 1); > > } > >=20=20 >=20> +static inline void set_page_count_as_frozen(struct page *page) > > +{ > > + set_page_count(page, 0); > > +} > > + > >=20 >=20This name is strange. Maybe something like init_page_count_frozen()? TBH I slightly dislike "init" in this naming, but it's probably better than our proposal. Maybe set_page_count_frozen()? > And don't you want to update it in patch 2 to set the bit? My bad, apologies. Don't even know how it passed stress-tests... > >=20 >=20> static inline void page_ref_add(struct page *page, int nr) > > { > > + VM_BUG_ON(__page_count_is_frozen(page_count(page))); > >=20 >=20Hm. These VM_BUG_ONs are useless after patch 2. >=20 >=20In patch 2, you make __page_count_is_frozen() check the frozen bit an= d > page_count() masks out frozen bit. >=20 >=20I guess you want to read raw ref number here, no? Yes, indeed. I will rewrite with __page_count_is_frozen(struct page *) > And why not VM_BUG_ON_PAGE/FOLIO()? Will change to those > >=20 >=20> atomic_add(nr, &page->_refcount); > > if (page_ref_tracepoint_active(page_ref_mod)) > > __page_ref_mod(page, nr); > >=20 >=20--=20 >=20 Kiryl Shutsemau / Kirill A. Shutemov >