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d=hostedemail.com; t=1753147412; a=rsa-sha256; cv=none; b=Ie87RGg3UzrSYd9/hRRJkI0Oqsv8I1NocHxYq8vYhYuSgDJiGXkP90KFSCN3TMcZhRNJE0 CAg9N1qCtX3vYu4WXoujTCuFlqqwaacHrXq1ZOjP9Me3+4pqJBwlLilNPkQPZN1lrdr/rU mgKVjFg2Br5DsD4nKIYKR3wdL1qWHJI= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf07.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com X-AuditID: a67dfc5b-681ff7000002311f-c0-687ee811fc6c Date: Tue, 22 Jul 2025 10:23:24 +0900 From: Byungchul Park To: Pavel Begunkov Cc: Mina Almasry , 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, 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, 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, ziy@nvidia.com, jackmanb@google.com Subject: Re: [PATCH net-next v9 3/8] page_pool: access ->pp_magic through struct netmem_desc in page_pool_page_is_pp() Message-ID: <20250722012324.GA63367@system.software.com> References: <20250710082807.27402-1-byungchul@sk.com> <20250710082807.27402-4-byungchul@sk.com> <20250711011435.GC40145@system.software.com> <582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com> <20250717030858.GA26168@system.software.com> MIME-Version: 1.0 Content-Type: text/plain; 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> > > > > + > > > > > + return (desc->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > > > > > +} > > > > > > > > pages can be pp pages (where they have pp fields inside of them) or > > > > non-pp pages (where they don't have pp fields inside them, because > > > > they were never allocated from the page_pool). > > > > > > > > Casting a page to a netmem_desc, and then checking if the page was a > > > > pp page doesn't makes sense to me on a fundamental level. The > > > > netmem_desc is only valid if the page was a pp page in the first > > > > place. Maybe page_to_nmdesc should reject the cast if the page is not > > > > a pp page or something. > > > > > > Right, as you already know, the current mainline code already has the > > > same problem but we've been using the werid way so far, in other words, > > > mm code is checking if it's a pp page or not by using ->pp_magic, but > > > it's ->lur, ->buddy_list, or ->pcp_list if it's not a pp page. > > > > > > Both the mainline code and this patch can make sense *only if* it's > > > actually a pp page. It's unevitable until mm provides a way to identify > > > the type of page for page pool. Thoughts? > > Question to mm folks, can we add a new PGTY for page pool and use > > that to filter page pool originated pages? Like in the incomplete > > and untested diff below? > > > > > > commit 8fc2347fb3ff4a3fc7929c70a5a21e1128935d4a > > Author: Pavel Begunkov > > Date: Sat Jul 12 14:29:52 2025 +0100 > > > > net/mm: use PGTY for tracking page pool pages > > > > Currently, we use page->pp_magic to determine whether a page belongs to > > a page pool. It's not ideal as the field is aliased with other page > > types, and thus needs to to rely on elaborated rules to work. Add a new > > page type for page pool. > > Hi Pavel, > > I need this work to be done to remove ->pp_magic in struct page. Will > you let me work on this work? Or can you please refine and post this No response I got. Thus, I started. I hope you understand. Byungchul > work? If you let me, I will go for this as a separate patch from this > series. > > Byungchul > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 0ef2ba0c667a..975a013f1f17 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -4175,7 +4175,7 @@ int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status); > > #ifdef CONFIG_PAGE_POOL > > static inline bool page_pool_page_is_pp(struct page *page) > > { > > - return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE; > > + return PageNetpp(page); > > } > > #else > > static inline bool page_pool_page_is_pp(struct page *page) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > > index 4fe5ee67535b..9bd1dfded2fc 100644 > > --- a/include/linux/page-flags.h > > +++ b/include/linux/page-flags.h > > @@ -957,6 +957,7 @@ enum pagetype { > > PGTY_zsmalloc = 0xf6, > > PGTY_unaccepted = 0xf7, > > PGTY_large_kmalloc = 0xf8, > > + PGTY_netpp = 0xf9, > > > > PGTY_mapcount_underflow = 0xff > > }; > > @@ -1101,6 +1102,11 @@ PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc) > > PAGE_TYPE_OPS(Unaccepted, unaccepted, unaccepted) > > FOLIO_TYPE_OPS(large_kmalloc, large_kmalloc) > > > > +/* > > + * Marks page_pool allocated pages > > + */ > > +PAGE_TYPE_OPS(Netpp, netpp, netpp) > > + > > /** > > * PageHuge - Determine if the page belongs to hugetlbfs > > * @page: The page to test. > > diff --git a/include/net/netmem.h b/include/net/netmem.h > > index de1d95f04076..20f5dbb08149 100644 > > --- a/include/net/netmem.h > > +++ b/include/net/netmem.h > > @@ -113,6 +113,8 @@ static inline bool netmem_is_net_iov(const netmem_ref netmem) > > */ > > static inline struct page *__netmem_to_page(netmem_ref netmem) > > { > > + DEBUG_NET_WARN_ON_ONCE(netmem_is_net_iov(netmem)); > > + > > return (__force struct page *)netmem; > > } > > > > diff --git a/net/core/netmem_priv.h b/net/core/netmem_priv.h > > index cd95394399b4..e38c64da1a78 100644 > > --- a/net/core/netmem_priv.h > > +++ b/net/core/netmem_priv.h > > @@ -13,16 +13,11 @@ static inline void netmem_or_pp_magic(netmem_ref netmem, unsigned long pp_magic) > > __netmem_clear_lsb(netmem)->pp_magic |= pp_magic; > > } > > > > -static inline void netmem_clear_pp_magic(netmem_ref netmem) > > -{ > > - WARN_ON_ONCE(__netmem_clear_lsb(netmem)->pp_magic & PP_DMA_INDEX_MASK); > > - > > - __netmem_clear_lsb(netmem)->pp_magic = 0; > > -} > > - > > static inline bool netmem_is_pp(netmem_ref netmem) > > { > > - return (netmem_get_pp_magic(netmem) & PP_MAGIC_MASK) == PP_SIGNATURE; > > + if (netmem_is_net_iov(netmem)) > > + return true; > > + return page_pool_page_is_pp(netmem_to_page(netmem)); > > } > > > > static inline void netmem_set_pp(netmem_ref netmem, struct page_pool *pool) > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > > index 05e2e22a8f7c..52120e2912a6 100644 > > --- a/net/core/page_pool.c > > +++ b/net/core/page_pool.c > > @@ -371,6 +371,13 @@ struct page_pool *page_pool_create(const struct page_pool_params *params) > > } > > EXPORT_SYMBOL(page_pool_create); > > > > +static void page_pool_set_page_pp_info(struct page_pool *pool, > > + struct page *page) > > +{ > > + __SetPageNetpp(page); > > + page_pool_set_pp_info(page_to_netmem(page)); > > +} > > + > > static void page_pool_return_netmem(struct page_pool *pool, netmem_ref netmem); > > > > static noinline netmem_ref page_pool_refill_alloc_cache(struct page_pool *pool) > > @@ -534,7 +541,7 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool, > > } > > > > alloc_stat_inc(pool, slow_high_order); > > - page_pool_set_pp_info(pool, page_to_netmem(page)); > > + page_pool_set_page_pp_info(pool, page); > > > > /* Track how many pages are held 'in-flight' */ > > pool->pages_state_hold_cnt++; > > @@ -579,7 +586,7 @@ static noinline netmem_ref __page_pool_alloc_netmems_slow(struct page_pool *pool > > continue; > > } > > > > - page_pool_set_pp_info(pool, netmem); > > + page_pool_set_page_pp_info(pool, __netmem_to_page(netmem)); > > pool->alloc.cache[pool->alloc.count++] = netmem; > > /* Track how many pages are held 'in-flight' */ > > pool->pages_state_hold_cnt++; > > @@ -654,7 +661,6 @@ s32 page_pool_inflight(const struct page_pool *pool, bool strict) > > void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem) > > { > > netmem_set_pp(netmem, pool); > > - netmem_or_pp_magic(netmem, PP_SIGNATURE); > > > > /* Ensuring all pages have been split into one fragment initially: > > * page_pool_set_pp_info() is only called once for every page when it > > @@ -669,7 +675,6 @@ void page_pool_set_pp_info(struct page_pool *pool, netmem_ref netmem) > > > > void page_pool_clear_pp_info(netmem_ref netmem) > > { > > - netmem_clear_pp_magic(netmem); > > netmem_set_pp(netmem, NULL); > > } > > > > @@ -730,8 +735,11 @@ static void page_pool_return_netmem(struct page_pool *pool, netmem_ref netmem) > > trace_page_pool_state_release(pool, netmem, count); > > > > if (put) { > > + struct page *page = netmem_to_page(netmem); > > + > > page_pool_clear_pp_info(netmem); > > - put_page(netmem_to_page(netmem)); > > + __ClearPageNetpp(page); > > + put_page(page); > > } > > /* An optimization would be to call __free_pages(page, pool->p.order) > > * knowing page is not part of page-cache (thus avoiding a > > > > -- > > Pavel Begunkov