From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from invmail4.hynix.com (exvmail4.skhynix.com [166.125.252.92]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 653BDAD2C; Mon, 23 Jun 2025 11:25:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=166.125.252.92 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750677944; cv=none; b=KqrEs2MjPXcH2QvUPkccMEjLBU5JXgq//xGzARWtqwr6zmfX5FvCOaYMpZ5ev3lgPweR4T9iGiq7rCYhNJLSdKkQIDoxF87WwE7HwdOtY2m1NICwL9ue35EUPmHp6pTXfCSrPpD39b1dBGZt7ZL3xou+dZqC4CxYorgfyh+4OaU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750677944; c=relaxed/simple; bh=AfGEXRx1HFoQszR4uv7ffzuBfSxCOCFfR097o41bj/U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cE9q6IJUCW2iWWeDkNP1MFuzcRSyWQ4eC1xkoYUVQEnwu+e0n7Xt/uvUgNmZuHyCsm9qf7dgRENlzFzCUcNlH4sg/BsW0oWYPD6QlASDSxaL1+m6AvFbAB72+fc8yXsd+rt2PIhK7y6HO9DO3FjlWsclAGnSy41B4KA0OEsgQws= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com; spf=pass smtp.mailfrom=sk.com; arc=none smtp.client-ip=166.125.252.92 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=sk.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=sk.com X-AuditID: a67dfc5b-681ff7000002311f-80-685939af5f24 Date: Mon, 23 Jun 2025 20:25:30 +0900 From: Byungchul Park To: Zi Yan Cc: David Hildenbrand , willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, kuba@kernel.org, almasrymina@google.com, ilias.apalodimas@linaro.org, harry.yoo@oracle.com, hawk@kernel.org, akpm@linux-foundation.org, davem@davemloft.net, john.fastabend@gmail.com, andrew+netdev@lunn.ch, asml.silence@gmail.com, toke@redhat.com, tariqt@nvidia.com, edumazet@google.com, pabeni@redhat.com, saeedm@nvidia.com, leon@kernel.org, ast@kernel.org, daniel@iogearbox.net, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com, hannes@cmpxchg.org, jackmanb@google.com Subject: Re: [PATCH net-next v6 9/9] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is_pp() Message-ID: <20250623112530.GA67291@system.software.com> References: <20250620041224.46646-1-byungchul@sk.com> <20250620041224.46646-10-byungchul@sk.com> <20250623101622.GB3199@system.software.com> <460ACE40-9E99-42B8-90F0-2B18D2D8C72C@nvidia.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <460ACE40-9E99-42B8-90F0-2B18D2D8C72C@nvidia.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA02Sa0hTYRjHeXfec3E5OK7bm1bCKgrpjtETiFQf4hAI0dWKyNVObTSnzLx1 tZQi03UVclqtxDQtlkud5oVa1jQDxUpnmpqpXTTFmWNeqJwS+e3H/7n8ng8PR8kLaF9Oozsu 6nVKrYKRYulP7/srzBv2qld/bg6ATPMjBvLdcZDTUUJDZl4xgl8jLSwMVdkZyLrnoiCzLgnD sHmUgu7XnSzkW0Kg/UEPhvKLVgo6r1QzkJo0RkHFSD8L50tyJVBfbKDh5mg2BdaEDhbePctk oO3RHxp6bKkYaowPMbQbNsJr0xxw1fYhqDJbJeBKuc3AjQYTA1+S2hE0vOzEkHHOgMBc6aBh zD2xI+NVG7txsfCyb4ASCh82S4RS4ydWMFmihae5AUKyo4ESLHmXGMHivM4KrY3ljFB9awwL pSVDEiE1sZ8RBrs/YmGg8gMjmAs/YOGtqYrd5rNPGqQStZoYUb8qOEyqLsgaxpEXF8f1PvmF EtCP+cnIiyN8IDE4UyXJiJtkd85JT4z5JaSt/TvtYYZfShyOEcrDs3g/UmsYn2ApR/GFDHly oZH1FGbycWSss2eyScYDybFWTrKcdyOSXRkylfuQmvQu7GGKX05Ki1oZj5eaWJrzm5uK/Uli UcbkqBcfTJzJKYyHZ/OLyPNiu8TjJXw1R8rL7kim7p9HXuQ68FXkY5ymME5TGP8rjNMUJoTz kFyjiwlXarSBK9XxOk3cysMR4RY08UgPTo/vL0HO+h02xHNI4S0L8w5Vy2llTFR8uA0RjlLM ktk271bLZSpl/AlRH3FQH60Vo2zIj8OKubK1rliVnD+qPC4eE8VIUf+vKuG8fBPQwi3SA017 dDU7034k9W7KLvKveL87xHtR6Fb786D0xFPRdGL9Hzt7ZHvZ4GWtG6s+nr7RGzuybmBBBTNj 8BvvsyqWX9qRb695nPXG3WKN7N4ubaKO1DVdvhL4NdLrbmPo2TNH026LTl+p09VF26+lrJ/b WDacrvq82ly7bFdX86FYBY5SK9cEUPoo5V98/A9vRAMAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA02Sa0hTYRjHeXfOzo6jyXGtPGkoLCWKsoSiJ5KIoHpJ7OKHLn6xUx7c8tpW 4orEUoqW85JBNmcpovOWszWdE5OY5iUha6JYmStv2AUrb8xWmVMiv/34/5/n93x5aEKaL/Sj lYkXeVUiFy+nxKT4yJ6MrabdpxXbf3+XgcFUQ0G1KxWMHxqFYKhqQDAz/04E020dFJSWzBFg 6MkkYdb0k4Cx9mERVJsjwFk+TkLzTSsBwzmdFOgy3QQ8nZ8UwfXGCgG0FnUJ4VVDthDu/iwj wJr+QQS9TQYKhmoWhDBu15HQpa8kwZm9D9qL18Jc91cEbSarAOayiijIdxRTMJLpROBoHSah 8Fo2AlPLgBDcrkVH4fMh0b5g3Pr1G4EtlW8E2KZ/L8LF5kv4ScVmrB1wENhcdYvC5qk7IjzY 30zhzgI3iW2N0wKsy5ik8I+xtyT+1tJH4dKJ7wJssvSRx6RR4rAYPl6Zwqu27T0jVjwunSWT bwalfqmbQeno83otommW2cG6jFe0yIsmmWB2yPlJ6GGK2cgODMwTHpYx/mx39q9FFtMEY6HY uhv9Ik+xmkll3cPjS0MSBlijtWWJpYwLsWUtEcu5D9t1f5T0MMFsYW31g5TnLrEoNf6hl+NA NqO+cGnVi9nLTmmzKA+vYTawzxo6BLnIW7/CpF9h0v836VeYihFZhWTKxJQEThm/M0Qdp9Ak KlNDziUlmNHiq5Rf/ZXXiGZ6D9kRQyP5KklF+CmFVMilqDUJdsTShFwmse8/oZBKYjjNZV6V FK26FM+r7cifJuW+ksMn+TNSJpa7yMfxfDKv+tcKaC+/dFT7zK+nhObqIrW3w9odj3S6Wlpl Dts1FyOHkuM5nxb85WKfAwsf86IdvLXpxbrZAE1kR6/hbOiUZSQvqFl2nmp4520rnKQv2Hzv HfTSkOGDac6q8LyXORO8vKBAEJWw6ZDe3VH9AM/8jnVVjFpyHwYe9ePK0npf7++vDFhnlJNq BRe6mVCpub9KbC+1JgMAAA== X-CFilter-Loop: Reflected On Mon, Jun 23, 2025 at 07:13:21AM -0400, Zi Yan wrote: > On 23 Jun 2025, at 6:16, Byungchul Park wrote: > > On Mon, Jun 23, 2025 at 11:16:43AM +0200, David Hildenbrand wrote: > >> On 20.06.25 06:12, Byungchul Park wrote: > >>> To simplify struct page, the effort to separate its own descriptor from > >>> struct page is required and the work for page pool is on going. > >>> > >>> To achieve that, all the code should avoid directly accessing page pool > >>> members of struct page. > >>> > >>> Access ->pp_magic through struct netmem_desc instead of directly > >>> accessing it through struct page in page_pool_page_is_pp(). Plus, move > >>> page_pool_page_is_pp() from mm.h to netmem.h to use struct netmem_desc > >>> without header dependency issue. > >>> > >>> Signed-off-by: Byungchul Park > >>> Reviewed-by: Toke Høiland-Jørgensen > >>> Reviewed-by: Mina Almasry > >>> Reviewed-by: Pavel Begunkov > >>> Reviewed-by: Vlastimil Babka > >>> Acked-by: Harry Yoo > >>> --- > >>> include/linux/mm.h | 12 ------------ > >>> include/net/netmem.h | 14 ++++++++++++++ > >>> mm/page_alloc.c | 1 + > >>> 3 files changed, 15 insertions(+), 12 deletions(-) > >>> > >>> diff --git a/include/linux/mm.h b/include/linux/mm.h > >>> index 0ef2ba0c667a..0b7f7f998085 100644 > >>> --- a/include/linux/mm.h > >>> +++ b/include/linux/mm.h > >>> @@ -4172,16 +4172,4 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status); > >>> */ > >>> #define PP_MAGIC_MASK ~(PP_DMA_INDEX_MASK | 0x3UL) > >>> > >>> -#ifdef CONFIG_PAGE_POOL > >>> -static inline bool page_pool_page_is_pp(struct page *page) > >>> -{ > >>> - return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > >>> -} > >>> -#else > >>> -static inline bool page_pool_page_is_pp(struct page *page) > >>> -{ > >>> - return false; > >>> -} > >>> -#endif > >>> - > >>> #endif /* _LINUX_MM_H */ > >>> diff --git a/include/net/netmem.h b/include/net/netmem.h > >>> index d49ed49d250b..3d1b1dfc9ba5 100644 > >>> --- a/include/net/netmem.h > >>> +++ b/include/net/netmem.h > >>> @@ -56,6 +56,20 @@ NETMEM_DESC_ASSERT_OFFSET(pp_ref_count, pp_ref_count); > >>> */ > >>> static_assert(sizeof(struct netmem_desc) <= offsetof(struct page, _refcount)); > >>> > >>> +#ifdef CONFIG_PAGE_POOL > >>> +static inline bool page_pool_page_is_pp(struct page *page) > >>> +{ > >>> + struct netmem_desc *desc = (struct netmem_desc *)page; > >>> + > >>> + return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > >>> +} > >>> +#else > >>> +static inline bool page_pool_page_is_pp(struct page *page) > >>> +{ > >>> + return false; > >>> +} > >>> +#endif > >> > >> I wonder how helpful this cleanup is long-term. > >> > >> page_pool_page_is_pp() is only called from mm/page_alloc.c, right? > > > > Yes. > > > >> There, we want to make sure that no pagepool page is ever returned to > >> the buddy. > >> > >> How reasonable is this sanity check to have long-term? Wouldn't we be > >> able to check that on some higher-level freeing path? > >> > >> The reason I am commenting is that once we decouple "struct page" from > >> "struct netmem_desc", we'd have to lookup here the corresponding "struct > >> netmem_desc". > >> > >> ... but at that point here (when we free the actual pages), the "struct > >> netmem_desc" would likely already have been freed separately (remember: > >> it will be dynamically allocated). > >> > >> With that in mind: > >> > >> 1) Is there a higher level "struct netmem_desc" freeing path where we > >> could check that instead, so we don't have to cast from pages to > >> netmem_desc at all. > > > > I also thought it's too paranoiac. However, I thought it's other issue > > than this work. That's why I left the API as is for now, it can be gone > > once we get convinced the check is unnecessary in deep buddy. Wrong? > > > >> 2) How valuable are these sanity checks deep in the buddy? > > > > That was also what I felt weird on. > > It seems very useful when I asked last time[1]: > > |> We have actually used this at Cloudflare to catch some page_pool bugs. Indeed.. So I think it'd be better to leave the check as is until we will be fully convinced on that issue, I ideally agree with David's opinion tho. Byungchul > [1] https://lore.kernel.org/linux-mm/4d35bda2-d032-49db-bb6e-b1d70f10d436@kernel.org/ > > -- > Best Regards, > Yan, Zi