From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794768474; b=e2S5v97qA7iVwjuCXZjiPklzfrGlIRTMPNYpiF8s0DEyg0dLm2UR+bA1J+7S9OeStRVQ C9jb/Iebl6myqxXUcDLeAWOd+5eQ41wfiIEh10f8gJm2zU1aWVyrq5+AHIHraLNCfV7Yv pDgahMKUaF0yWcdNJ+zQ20xUU7RtDUPlPy4ZluZwih3tGbkS7iIz4Bcn5EFvZit080YSJ upIDile24B1K2vTQzEEWvVTQK8rHsGmdEB+oSOI3tavU8cQkpXRkmJG6mlCVVsLxPYu/z dQ/QkNKwQ+ASe4JFgOeENToYF4eQ5wtPDpD1sSsgFDgyICc7s/UpO9aAOKULFP400EQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794768474; h=Received:DKIM-Signature:From:To:Cc:Subject:In-Reply-To:References: Date:Message-ID:MIME-Version:Content-Type:Content-Transfer-Encoding; bh=vVIT0VvIfr5x7hfZPd3p28y+jJruOeCF2tb8ILdwEA0=; b=W//Cajl3sbKqHeopwx90vlwDHdBB04ME3QDUF8rdaSD5hj94bXI/VXfQcAW6xACSFhnl 3COeket+nT1n5/nWBRHZE1p5Eg4Dg4kl1tb2y4OApSLrRU2SOcc2nPfvXYFO5PyHeYamh KQ92fSqaAgzjWdpWTwndHcbDbUZ/fSgLzETjCCQDLupizFNzgziqLi8EMbWiCAr9IHNDK pOvbVJmySRUUG2F2VA+p93DNp1CxC+HUH90ihHrTbtOTR7uGzq1+hz4JPJRdMEUMak/UN /BcNubAykvdAEoynttvB61pqCH6xAUZ5OrngzAo1wfFSbuhFPuOZKzm47JI5mGs/lYw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=gnjywwDy; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 08908606A32C; Sun, 15 Nov 2026 18:47:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=gnjywwDy Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9FEB91F000C4; Sun, 15 Nov 2026 18:47:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794768473; bh=vVIT0VvIfr5x7hfZPd3p28y+jJruOeCF2tb8ILdwEA0=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=gnjywwDyy/1QOFuNOsVPOBmY0oUJnv/uxMTHgl3S317Jni12vFsFvxSJ61qmRThqA M5eFtD4v/rpELq8WGYNFP7QeWruxp3vRdH77cBLmWHTRXx2TYOY0kpXUiqJmMMgWty jZVFKRdrg/6OriBN3Joj2FWmhhlD3cGRU/jdGL04akelTdAzEWkuM0bdikTIKAubFw /ukQVE1ulZuxXEc0LEIDnjLbyR92xIoHxIC9RDQWUR2hVvNt88INllkoBbjpgj1IEU OLDFWnEh3tMHl83ES3li7ut5hFASgZ1XS1xRrbxkeWLqOzHMZYlGZj51lDVhUihMcN 4Xi8w5jxyrV6A== From: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= To: Stanislav Fomichev Cc: Magnus Karlsson , Maciej Fijalkowski , Stanislav Fomichev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Randy Dunlap , Alexander Duyck , kernel-team@meta.com, Andrew Lunn , Jesper Dangaard Brouer , Ilias Apalodimas , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Pavel Begunkov , Jens Axboe , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , netdev@vger.kernel.org, bpf@vger.kernel.org, io-uring@vger.kernel.org, Mina Almasry , "Mike Marciniszyn (Meta)" , Weiming Shi , Nikolay Aleksandrov , David Wei , Alexander Lobakin , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Stuart Clark Subject: Re: [PATCH net-next v1 02/11] net: Add memory provider capabilities In-Reply-To: References: <20261110102039.1002605-1-bjorn@kernel.org> <20261110102039.1002605-3-bjorn@kernel.org> <87mrrfa6c4.fsf@all.your.base.are.belong.to.us> <87cxsarvwd.fsf@all.your.base.are.belong.to.us> Date: Sun, 15 Nov 2026 19:47:50 +0100 Message-ID: <87bj7qj5ih.fsf@all.your.base.are.belong.to.us> 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=utf-8 Content-Transfer-Encoding: quoted-printable Stanislav Fomichev writes: > On 11/12, Bj=C3=B6rn T=C3=B6pel wrote: >> Stanislav Fomichev writes: >>=20 >> > On 11/11, Bj=C3=B6rn T=C3=B6pel wrote: >> >> Stanislav Fomichev writes: >> >> > On 11/10, Bj=C3=B6rn T=C3=B6pel wrote: >>=20 >> >> >> + if (static_branch_unlikely(&page_pool_mem_providers) && >> >> >> + WARN_ON_ONCE(!page_pool_supports_frag(pool))) >> >> >> + return 0; >> >> >> if (WARN_ON(size > max_size)) >> >> >> return 0; >> >> >>=20=20 >> >> > >> >> > What's the deal with that? How do we get here? >> >>=20 >> >> Hey! Thanks for taking a look at the series! >> >>=20 >> >> An explicit frag call on a whole-buffer provider is a driver bug: UMEM >> >> chunks can be smaller than a page, and RX gives the whole chunk to >> >> userspace. >> >>=20 >> >> But page_pool_alloc_netmem() also picks frags for small requests, so a >> >> valid call can warn. >> >>=20 >> >> I think it would be better to make it return a whole buffer and its >> >> actual size. The WARN stays in the frag API, before taking a new buff= er? >> >> Wdyt? >> > >> > I see.. Idk, I'd still return 0 here, but without a warn. Not sure >> > we want a warn for any api misuse? Returning no netmem is gonna be eno= ugh >> > to debug things? As for the calls from page_pool_alloc_netmem, I'd also >> > handle it explicitly? if (size > max_size || !page_pool_supports_frag)= ? >> > But no strong preference, up to you, was mostly trying to understand >> > what we are warning against here :-) >>=20 >> Yes, page_pool_alloc_netmem() gets the explicit check. Thanks! >>=20 >> For the frag API I'd keep a WARN_ON_ONCE, like the size check right >> below it. A silent 0 looks like an empty provider: the queue just >> stalls, and nothing points at the driver. With the helper fixed, only an >> explicit frag call on such a pool gets there... Wdyt? I'll probably take >> that route for v2. > > I guess, yeah, makes sense, let's return full size and warn. Maybe also > a short comment will help to explain why? Will do, with a comment! Bj=C3=B6rn