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smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BALjQ7oD; 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="BALjQ7oD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 24081C2BCB7; Wed, 13 May 2026 12:29:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778675399; bh=Dp/eLuCZ/1PTNaxErBFBY0x0xot4Fm2FxvmhaA8PCZc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=BALjQ7oDFiHFeFw/swgagdXwyAXHEQhvq/8j09YpSMbiWHgIF/jXoe/pCNizrAM/v hFRL2lXP0miBUe5oqwibjIWMYlciZV4HEwzOzpM6rnllo8wNHxQlO5SKy0YiN4GulC xjbNQqo+kMls8DI97Twpa9XUI6fDgyRuPN95wNRL57+uxS6Dpin0SycVE/seLD9eFc qUoYCPkrd7p0DTKkb5wfPfmQHQlcIEjKiatx5YcHQXmn0HKpcb2P1T9sTxVaMNVPDe c70L++s32jaqCU7kWQL7qX0TdAvtgN0iKmjPJC+8wQrGU62jt0CT4fWMzPwXgBP1Dk 6I1FUMsWR2XQw== Message-ID: <8348d867-f8a1-432c-be2d-699ad96b2e93@kernel.org> Date: Wed, 13 May 2026 14:29:46 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm: introduce a new page type for page pool in page type To: Byungchul Park , Dragos Tatulea Cc: linux-mm@kvack.org, akpm@linux-foundation.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, kuba@kernel.org, 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, 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 References: <20260224051347.19621-1-byungchul@sk.com> <982b9bc1-0a0a-4fc5-8e3a-3672db2b29a1@nvidia.com> <20260513121805.GA22430@system.software.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 5/13/26 14:18, Byungchul Park wrote: > On Wed, May 13, 2026 at 11:00:51AM +0200, Dragos Tatulea wrote: >> On 24.02.26 06:13, Byungchul Park wrote: >>> Currently, the condition 'page->pp_magic == PP_SIGNATURE' is used to >>> determine if a page belongs to a page pool. However, with the planned >>> removal of @pp_magic, we should instead leverage the page_type in struct >>> page, such as PGTY_netpp, for this purpose. >>> >>> Introduce and use the page type APIs e.g. PageNetpp(), __SetPageNetpp(), >>> and __ClearPageNetpp() instead, and remove the existing APIs accessing >>> @pp_magic e.g. page_pool_page_is_pp(), netmem_or_pp_magic(), and >>> netmem_clear_pp_magic(). >>> >>> Plus, add @page_type to struct net_iov at the same offset as struct page >>> so as to use the page_type APIs for struct net_iov as well. While at it, >>> reorder @type and @owner in struct net_iov to avoid a hole and >>> increasing the struct size. >>> >>> This work was inspired by the following link: >>> >>> https://lore.kernel.org/all/582f41c0-2742-4400-9c81-0d46bf4e8314@gmail.com/ >>> >>> While at it, move the sanity check for page pool to on the free path. >>> >>> Suggested-by: David Hildenbrand >>> Co-developed-by: Pavel Begunkov >>> Signed-off-by: Pavel Begunkov >>> Signed-off-by: Byungchul Park >>> Acked-by: David Hildenbrand >>> Acked-by: Zi Yan >>> Acked-by: Vlastimil Babka >>> Reviewed-by: Toke Høiland-Jørgensen >>> --- >> >> Seems like this patch broke tcp_mmap because >> validate_page_before_insert() returns -EINVAL due >> to a page having a type. Here's the full flow: >> >> getsockopt(TCP_ZEROCOPY_RECEIVE) returns -EINVAL because of the >> below flow in the kernel: >> >> tcp_zerocopy_receive() >> -> tcp_zerocopy_vm_insert_batch() >> -> vm_insert_pages() >> -> insert_pages() >> -> insert_page_in_batch_locked() >> -> validate_page_before_insert() returns -EINVAL >> because page_has_type(page) is now true. >> >> The patch below fixes the issue. But is this a valid fix? > > Hi, > > The problem comes from the fact that page_type and _mapcount are > union'ed but there is a case where these two information should be kept > at the same time. > > Why don't we allow these two information can be kept in the 4 bytes at > the same time until Zi Yan's work on _mapcount and page_type will be > done, instead of taking a step back? > > It can be more optimized but I suggest the approach I just mentioned: > --- > diff --git a/fs/proc/internal.h b/fs/proc/internal.h > index 64dc44832808..e5ec204866dc 100644 > --- a/fs/proc/internal.h > +++ b/fs/proc/internal.h > @@ -185,8 +185,7 @@ static inline int folio_precise_page_mapcount(struct folio *folio, > { > int mapcount = atomic_read(&page->_mapcount) + 1; > > - if (page_mapcount_is_type(mapcount)) > - mapcount = 0; > + mapcount = page_mapcount_clear_type(mapcount); > if (folio_test_large(folio)) > mapcount += folio_entire_mapcount(folio); > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 8260e28205e9..f45064796313 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1865,8 +1865,7 @@ static inline int folio_mapcount(const struct folio *folio) > > if (likely(!folio_test_large(folio))) { > mapcount = atomic_read(&folio->_mapcount) + 1; > - if (page_mapcount_is_type(mapcount)) > - mapcount = 0; > + mapcount = page_mapcount_clear_type(mapcount); > return mapcount; > } > return folio_large_mapcount(folio); > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 0e03d816e8b9..f3b0d1fa262d 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -934,9 +934,9 @@ static inline bool page_type_has_type(int page_type) > } > > /* This takes a mapcount which is one more than page->_mapcount */ > -static inline bool page_mapcount_is_type(unsigned int mapcount) > +static inline unsigned int page_mapcount_clear_type(unsigned int mapcount) > { > - return page_type_has_type(mapcount - 1); > + return (unsigned int)(((int)(mapcount << 8)) >> 8); > } > > static inline bool page_has_type(const struct page *page) > @@ -953,16 +953,20 @@ static __always_inline void __folio_set_##fname(struct folio *folio) \ > { \ > if (folio_test_##fname(folio)) \ > return; \ > - VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX, \ > + VM_BUG_ON_FOLIO(page_type_has_type(data_race(folio->page.page_type)), \ > folio); \ > - folio->page.page_type = (unsigned int)PGTY_##lname << 24; \ > + folio->page.page_type &= ~(PGTY_mapcount_underflow << 24); \ > + folio->page.page_type |= (unsigned int)PGTY_##lname << 24; \ > } \ > static __always_inline void __folio_clear_##fname(struct folio *folio) \ > { \ > - if (folio->page.page_type == UINT_MAX) \ > + int mapcount; \ > + \ > + if (!page_type_has_type(folio->page.page_type)) \ > return; \ > VM_BUG_ON_FOLIO(!folio_test_##fname(folio), folio); \ > - folio->page.page_type = UINT_MAX; \ > + mapcount = atomic_read(&folio->page._mapcount); \ > + folio->page.page_type = page_mapcount_clear_type(mapcount); \ > } > > #define PAGE_TYPE_OPS(uname, lname, fname) \ > @@ -975,15 +979,20 @@ static __always_inline void __SetPage##uname(struct page *page) \ > { \ > if (Page##uname(page)) \ > return; \ > - VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page); \ > - page->page_type = (unsigned int)PGTY_##lname << 24; \ > + VM_BUG_ON_PAGE(page_type_has_type(data_race(page->page_type)), \ > + page); \ > + page->page_type &= ~(PGTY_mapcount_underflow << 24); \ > + page->page_type |= (unsigned int)PGTY_##lname << 24; \ > } \ > static __always_inline void __ClearPage##uname(struct page *page) \ > { \ > - if (page->page_type == UINT_MAX) \ > + int mapcount; \ > + \ > + if (!page_type_has_type(page->page_type)) \ > return; \ > VM_BUG_ON_PAGE(!Page##uname(page), page); \ > - page->page_type = UINT_MAX; \ > + mapcount = atomic_read(&page->_mapcount); \ > + page->page_type = page_mapcount_clear_type(mapcount); \ > } > > /* > diff --git a/mm/debug.c b/mm/debug.c > index 77fa8fe1d641..9a932ded09d4 100644 > --- a/mm/debug.c > +++ b/mm/debug.c > @@ -74,8 +74,7 @@ static void __dump_folio(const struct folio *folio, const struct page *page, > int mapcount = atomic_read(&page->_mapcount) + 1; > char *type = ""; > > - if (page_mapcount_is_type(mapcount)) > - mapcount = 0; > + mapcount = page_mapcount_clear_type(mapcount); > > pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n", > folio_ref_count(folio), mapcount, mapping, > --- > > Thoughts? God no. -- Cheers, David