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s=arc-20220608; d=hostedemail.com; t=1778674694; a=rsa-sha256; cv=none; b=lsSsqCAkWeHlQ8kxEkzgpKKgFyic5zYT/KJd8Dj3NQzRo7bhCa4YipQZeBa/pGdjfUiHv+ NRVmDoK6KLweuLbDMJ5623ERAM1Rgy+yitzBtgNHyM2Q+sgwt1RaA7XOaEXN6ebA6hIe1O bbGWZLN31UdzJBDm4NMRUrhX0Of4N4A= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=none; spf=pass (imf20.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none X-AuditID: a67dfc5b-c2dff70000001609-3c-6a046c0274bd Date: Wed, 13 May 2026 21:18:05 +0900 From: Byungchul Park To: 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, 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 Subject: Re: [PATCH v4] mm: introduce a new page type for page pool in page type Message-ID: <20260513121805.GA22430@system.software.com> References: <20260224051347.19621-1-byungchul@sk.com> <982b9bc1-0a0a-4fc5-8e3a-3672db2b29a1@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; 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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? Byungchul > diff --git a/mm/memory.c b/mm/memory.c > index ea6568571131..4cb12673f450 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2326,7 +2326,7 @@ static int validate_page_before_insert(struct vm_area_struct *vma, > return -EINVAL; > return 0; > } > - if (folio_test_anon(folio) || page_has_type(page)) > + if (folio_test_anon(folio) || (page_has_type(page) && !PageNetpp(page))) > return -EINVAL; > flush_dcache_folio(folio); > return 0; > > Thanks, > Dragos >