From: Byungchul Park <byungchul@sk•com>
To: Dragos Tatulea <dtatulea@nvidia•com>
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
Date: Wed, 13 May 2026 21:18:05 +0900 [thread overview]
Message-ID: <20260513121805.GA22430@system.software.com> (raw)
In-Reply-To: <982b9bc1-0a0a-4fc5-8e3a-3672db2b29a1@nvidia.com>
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 <david@redhat•com>
> > Co-developed-by: Pavel Begunkov <asml.silence@gmail•com>
> > Signed-off-by: Pavel Begunkov <asml.silence@gmail•com>
> > Signed-off-by: Byungchul Park <byungchul@sk•com>
> > Acked-by: David Hildenbrand <david@redhat•com>
> > Acked-by: Zi Yan <ziy@nvidia•com>
> > Acked-by: Vlastimil Babka <vbabka@suse•cz>
> > Reviewed-by: Toke Høiland-Jørgensen <toke@redhat•com>
> > ---
>
> 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
>
next prev parent reply other threads:[~2026-05-13 12:18 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-24 5:13 [PATCH v4] mm: introduce a new page type for page pool in page type Byungchul Park
2026-02-25 7:19 ` Mike Rapoport
2026-02-26 18:49 ` Johannes Weiner
2026-03-16 22:29 ` Byungchul Park
2026-03-16 22:31 ` [PATCH v5] " Byungchul Park
2026-03-17 9:20 ` Jesper Dangaard Brouer
2026-03-17 10:03 ` Ilias Apalodimas
2026-03-17 11:06 ` Dragos Tatulea
2026-03-19 23:31 ` Jakub Kicinski
2026-03-18 2:02 ` Byungchul Park
2026-03-20 11:44 ` Jesper Dangaard Brouer
2026-03-23 12:16 ` Ilias Apalodimas
2026-03-19 23:31 ` Jakub Kicinski
2026-05-13 9:00 ` [PATCH v4] " Dragos Tatulea
2026-05-13 9:12 ` Vlastimil Babka (SUSE)
2026-05-13 9:26 ` Pedro Falcato
2026-05-13 9:36 ` David Hildenbrand (Arm)
2026-05-13 12:06 ` Dragos Tatulea
2026-05-13 12:11 ` David Hildenbrand (Arm)
2026-05-14 8:54 ` Byungchul Park
2026-05-14 9:24 ` Dragos Tatulea
2026-05-15 0:01 ` Byungchul Park
2026-05-13 9:34 ` David Hildenbrand (Arm)
2026-05-13 12:18 ` Byungchul Park [this message]
2026-05-13 12:29 ` David Hildenbrand (Arm)
2026-05-13 12:39 ` Byungchul Park
2026-05-13 13:02 ` David Hildenbrand (Arm)
2026-05-13 13:26 ` Byungchul Park
2026-05-18 9:33 ` David Hildenbrand (Arm)
2026-05-13 9:42 ` Lorenzo Stoakes
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