From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 73878219A86; Fri, 7 Nov 2025 02:08:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762481294; cv=none; b=fWqBkbWKEXoJpJZVph1EJQptGaUMnVkLxHeQWN84yOGgJbNVcmtODonj1+nTW4cpg7OI7gyR8uYfe7Q/e3DwrdTcv3SGylQJ7Wm9tDYf1CPio7ovHPONVr7Ff0q7bfvwURmyC31r/TWiMTgznjIRkghlkXJIBktNxwzzOmf6q/E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762481294; c=relaxed/simple; bh=krN2HbEAPJ9LZ7iRNlMAlG+UbT7YoouhmyVRCR+YH4U=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=SS+w3b6dh4/uYgpPQR7wB/1j0n5R5Pt5hOA4OziLeWVEyLFtDPwSa5JchLi7sJ7lV6ghU00z5usOYc04C43ok/a6OS47NOmuFptjOCBkUEF8RBFLuJYYHF4ML9Njc80K632D40MIoS8JmRkohVAq87WZkTSCvYePJ2GSWmKwxPQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NCm/SkLf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NCm/SkLf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A1FB7C4CEFB; Fri, 7 Nov 2025 02:08:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762481294; bh=krN2HbEAPJ9LZ7iRNlMAlG+UbT7YoouhmyVRCR+YH4U=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=NCm/SkLf0sDAsmYdC0ji01eys0nbyjJVvHg3S7lgfslaEnD9BVkC/1GHvsGoJdtcD 6aFFfWl+eRdUa2P1IoiFv7Dm4LKqOdxkMEjcj0D7G9kE/QdBQjWl01CAqqMZlLk9gU OEKganv0Zc9V1YeZc8eewaAHC8E6S3BmHqVXJEkNXfY4ZohJUOvegj8GstXxpWV+dS bH8w8zRnLdd3MBCHEQhkcLSEgwh0QK8DGVApLdJqeFVKnO8+KZWlbOHbJo4Z8UCy0l q3fLPgBC9KjsOaNAodtNomC/uutUVR/IkxCfXaDgb5L4m5cwdnNmIfHePUsmOlTYTk t9ibqp7zouV1Q== Date: Thu, 6 Nov 2025 18:08:10 -0800 From: Jakub Kicinski To: Byungchul Park Cc: linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel_team@skhynix.com, harry.yoo@oracle.com, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, saeedm@nvidia.com, leon@kernel.org, tariqt@nvidia.com, mbloch@nvidia.com, andrew+netdev@lunn.ch, edumazet@google.com, pabeni@redhat.com, akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, ilias.apalodimas@linaro.org, willy@infradead.org, brauner@kernel.org, kas@kernel.org, yuzhao@google.com, usamaarif642@gmail.com, baolin.wang@linux.alibaba.com, almasrymina@google.com, toke@redhat.com, asml.silence@gmail.com, bpf@vger.kernel.org, linux-rdma@vger.kernel.org, sfr@canb.auug.org.au, dw@davidwei.uk, ap420073@gmail.com, dtatulea@nvidia.com Subject: Re: [RFC mm v5 1/2] page_pool: check nmdesc->pp to see its usage as page pool for net_iov not page-backed Message-ID: <20251106180810.6b06f71a@kernel.org> In-Reply-To: <20251107015902.GA3021@system.software.com> References: <20251103075108.26437-1-byungchul@sk.com> <20251103075108.26437-2-byungchul@sk.com> <20251106173320.2f8e683a@kernel.org> <20251107015902.GA3021@system.software.com> Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 7 Nov 2025 10:59:02 +0900 Byungchul Park wrote: > > > page-backed, the identification cannot be based on the page_type. > > > Instead, nmdesc->pp can be used to see if it belongs to a page pool, by > > > making sure nmdesc->pp is NULL otherwise. > > > > Please explain why. Isn't the type just a value in a field? > > Which net_iov could also set accordingly.. ? > > page_type field is in 'struct page', so 'struct page' can check the type. > > However, the field is not in 'struct net_iov', so 'struct net_iov' that > is not backed by page, cannot use the type checking to see if it's page > pool'ed instance. > > I'm afraid I didn't get your questions. I will try to explain again > properly if you give me more detail and example about your questions or > requirement. net_iov has members in the same place as page. page_type is just a field right now. static __always_inline int Page##uname(const struct page *page) \ { \ return data_race(page->page_type >> 24) == PGTY_##lname; \ } \ The whole thing works right now by overlaying one struct on top of another, and shared members being in the same places. Is this clear enough?