From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from invmail4.hynix.com (exvmail4.hynix.com [166.125.252.92]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8984238E5DC; Wed, 13 May 2026 12:18:18 +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=1778674704; cv=none; b=AUZR8rNrN5nPfn9Hx0zxMr1hi2ghcPd7P+94GVPzEe+uyCc4fx5wTBg/XuJACXFs7yUikZfbCcccK/405yVd0kqLZKK6coFR2ajKiBecZb39CCI2gk9Ex1uDCYUSxvCBcPOZjkGZQgEy4zrRGt8AM/OQ2bB7Pml3ZFy8luljIAk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778674704; c=relaxed/simple; bh=V+k0jlwcI8Q8Y1VYcQSmvuiN0PkI27SnbPw/BmTICW4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QNSSKhZGSVwW7TbF60i0ZoZ/VB0G1GKLtvYoX9fzbeuXNWAheiW91n+PxM/gT6IxUorv6L3rxEvhcRiUffaFXZqAJNr/asO3FkcLzwzCLxyAZXq16c1AUALnIPMW8QCQaro1yw3tfaU+dE3P2Bqk7r7bdEbmqTQ3FGtbFunplKE= 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-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> 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: <982b9bc1-0a0a-4fc5-8e3a-3672db2b29a1@nvidia.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA02SbUxTVxjHc+49PffS2ORYEA6aZVuXRYMKU/nwmKhxH0YOS0y2uU9b4mzk xpa1VVtgYGJWhERhUlDnBhe2wIyIiGCqhRbFVEBAljDsoquhCqsKGW86cFVepqMQM7798n+e /H/Ph0cW9WHNatlsy1LsNqPFQLRYO7Hil42CBWd+UPR3KlQ1NRC4+DIXzg95NTDTMCJAVX0z guczAxK8butCMN3ZTWCsYwrB2ZqICFW/FWL4p2lWBF/rCILR8ksEnnSFJbjo3gWDtcMYrh9r ESFc2kOgpHBOhLaZSQmOeusWiq84Jehvdmng+9lzIrQ4hyT4vbWKwMOG1xoYbi/BcFu9gOHZ mU4RBl07oas6HiK/jiPobGoRIHLiJwJ3K1oF8LTdleB0oJrAo8JBBIGOMIYz88cJVOa7EMy9 XKicLHuugcpbD6WdyTw/GCS8Y/ypyK9euC/we+UnMQ/e6BW4T30g8Wp3Nr9Sl8SLgwGRu+uL CHdPnZJ46N51wnvK5zD3/bmV+7zTAi8pmCSfrPpCuy1DsZhzFHvKjr1aU/lfHeTgja25/tkX ghMVJhejGJnRVBb64Zb4hnsmzi0ypu8zf6RGiDKha1kwOLOYx9F1zOk5jYuRVhbpqMQG7rg1 0UEs/Yz1qpWLSzoKTL3qXmBZ1lMzG7i0dyleyW5XPMZRFukG5vOESHRFpGvY+VfyUvw2K/As tcTQHWygsYJEeRV9j/mbu4WoltGCGBZyzWmWbk5kN+uCuAytVJcp1GUK9X+FukxRjXA90ptt OVaj2ZKabMqzmXOT9x2wutHC59Uemf/Si6b6d7cjKiPDCp1/P87Ua4w5jjxrO2KyaIjTlXah TL0uw5h3WLEf+MqebVEc7WiNjA0Jus2RbzL0dL8xS/laUQ4q9jdTQY5Z7UTmRu0ftWnp6fMf h/L9ifK2U/1nay47sn9uTexdrzTHDqf8q+5JSXu0h5q/85qOpXxa23g44fPNE6+sNtQdG8gd zE4rfWu7MevQ0Mai0Y8qp9edHCspe/fak138pnVEzfgx4cM+U9z99L4T9Gl80rfj7xwqGlvL XYFwQfyGvu3pWzy7DdhhMm5KEu0O439C5sGzdQMAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA02Sf0yMcRzHfZ/nue/zdHP2OOE7+bVrxqL8ynz8mGUtvgwzTFuMjp7p6jrc VSsWl5ofN0V+zHVli1Qk2k6/rhXnrjvFH5Kxs4tImCRGRWXSaab/Xnu/33v99RZYZYNsiqDR JUp6nVqrwnJOvmlFRjCj5eIWuDsCIb+8DMPNnylQ8rpGBv1lHxjIL61C0NPv5WGo3o3ge8MD DJ+c3xAUXuljIf9xJge95QMs2Go/IOg038Lwzt3Ow03rRmgrfs9B3YlqFtrPNGLIyhxkob6/ m4djNdeHxXeMPDgvN8mguSpbBhcGilioNr7m4WltPoZXZUMyeO/I4qDJcoODrxcbWGjLDgN3 wSToe9SFoKG8moG+05cxPMutZaCy/hkP51sKMLzNbEPQ4mzn4OKvkxjy0rMRDP4cVnaf7ZFB nusVHzafpns8mDq7vrC04sYLhj4353DUc/chQ22WlzwtsCbRO9eDqMnTwlJr6SlMrd/O8bT1 eR2mjeZBjtreLKO2mu8MzcroxpsnRclXxkhaTbKkn78qWh5r/ujEB+4uS7EP/GCMKDPEhPwE IoaSxs9FrI85cRax911hfIzF2cTj6f+b+4tziLHyPGdCcoEVO3nifWKV+YoJ4hby0JL3d6QQ gVgqrMMsCEpRQ7y3okfi8aQpt4PzMSvOI7bKVuybsGIAKfktjMQzSEbliMVPXEW8t3OxjyeK gcRe9YA5i8ZZRpkso0yW/ybLKFMB4kqRv0aXnKDWaJeEGOJjU3WalJC9+xOsaPhbxWm/cmpQ z9O1DiQKSDVWYd/HxSll6mRDaoIDEYFV+SvOuFGcUhGjTj0k6ffv1idpJYMDBQicarJifaQU rRT3qROleEk6IOn/tYzgN8WI7Iejkk3HSaHLuWFOW1pSZPXWiLnTdlnnrom49js8sm5WqvJ0 77bgsuYJuyeve3l/dY7uTZbjcGjH0u24l5k2rtWVXryHmobu32MvGYPT0rfZjlSEH/WrWj8m dPGOHVOHdhrNAXpvTKfr5PSZV7vehpVEPg6P2LkoYdMhF7/44PK4xEQVZ4hVLwxi9Qb1H0DS Hk1XAwAA X-CFilter-Loop: Reflected 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? 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 >