netdev - Re: [PATCH net-next v7 1/2] page_pool: Move pp

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Message-ID: <87cydoxsgs.fsf@toke.dk>
Date: Mon, 07 Apr 2025 10:53:55 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Zi Yan <ziy@...dia.com>, "David S. Miller" <davem@...emloft.net>, Jakub
 Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
 Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Ilias
 Apalodimas <ilias.apalodimas@...aro.org>, Simon Horman <horms@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>, Mina Almasry
 <almasrymina@...gle.com>, Yonglong Liu <liuyonglong@...wei.com>, Yunsheng
 Lin <linyunsheng@...wei.com>, Pavel Begunkov <asml.silence@...il.com>,
 Matthew Wilcox <willy@...radead.org>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH net-next v7 1/2] page_pool: Move pp_magic check into
 helper functions

"Zi Yan" <ziy@...dia.com> writes:

> On Fri Apr 4, 2025 at 6:18 AM EDT, Toke Høiland-Jørgensen wrote:
>> Since we are about to stash some more information into the pp_magic
>> field, let's move the magic signature checks into a pair of helper
>> functions so it can be changed in one place.
>>
>> Reviewed-by: Mina Almasry <almasrymina@...gle.com>
>> Tested-by: Yonglong Liu <liuyonglong@...wei.com>
>> Acked-by: Jesper Dangaard Brouer <hawk@...nel.org>
>> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>>  drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c |  4 ++--
>>  include/net/page_pool/types.h                    | 18 ++++++++++++++++++
>>  mm/page_alloc.c                                  |  9 +++------
>>  net/core/netmem_priv.h                           |  5 +++++
>>  net/core/skbuff.c                                | 16 ++--------------
>>  net/core/xdp.c                                   |  4 ++--
>>  6 files changed, 32 insertions(+), 24 deletions(-)
>>
>
> <snip>
>
>> diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
>> index 36eb57d73abc6cfc601e700ca08be20fb8281055..df0d3c1608929605224feb26173135ff37951ef8 100644
>> --- a/include/net/page_pool/types.h
>> +++ b/include/net/page_pool/types.h
>> @@ -54,6 +54,14 @@ struct pp_alloc_cache {
>>  	netmem_ref cache[PP_ALLOC_CACHE_SIZE];
>>  };
>>  
>> +/* Mask used for checking in page_pool_page_is_pp() below. page->pp_magic is
>> + * OR'ed with PP_SIGNATURE after the allocation in order to preserve bit 0 for
>> + * the head page of compound page and bit 1 for pfmemalloc page.
>> + * page_is_pfmemalloc() is checked in __page_pool_put_page() to avoid recycling
>> + * the pfmemalloc page.
>> + */
>> +#define PP_MAGIC_MASK ~0x3UL
>> +
>>  /**
>>   * struct page_pool_params - page pool parameters
>>   * @fast:	params accessed frequently on hotpath
>> @@ -264,6 +272,11 @@ void page_pool_destroy(struct page_pool *pool);
>>  void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
>>  			   const struct xdp_mem_info *mem);
>>  void page_pool_put_netmem_bulk(netmem_ref *data, u32 count);
>> +
>> +static inline bool page_pool_page_is_pp(struct page *page)
>> +{
>> +	return (page->pp_magic & PP_MAGIC_MASK) == PP_SIGNATURE;
>> +}
>>  #else
>>  static inline void page_pool_destroy(struct page_pool *pool)
>>  {
>> @@ -278,6 +291,11 @@ static inline void page_pool_use_xdp_mem(struct page_pool *pool,
>>  static inline void page_pool_put_netmem_bulk(netmem_ref *data, u32 count)
>>  {
>>  }
>> +
>> +static inline bool page_pool_page_is_pp(struct page *page)
>> +{
>> +	return false;
>> +}
>>  #endif
>>  
>>  void page_pool_put_unrefed_netmem(struct page_pool *pool, netmem_ref netmem,
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index f51aa6051a99867d2d7d8c70aa7c30e523629951..347a3cc2c188f4a9ced85e0d198947be7c503526 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -55,6 +55,7 @@
>>  #include <linux/delayacct.h>
>>  #include <linux/cacheinfo.h>
>>  #include <linux/pgalloc_tag.h>
>> +#include <net/page_pool/types.h>
>>  #include <asm/div64.h>
>>  #include "internal.h"
>>  #include "shuffle.h"
>> @@ -897,9 +898,7 @@ static inline bool page_expected_state(struct page *page,
>>  #ifdef CONFIG_MEMCG
>>  			page->memcg_data |
>>  #endif
>> -#ifdef CONFIG_PAGE_POOL
>> -			((page->pp_magic & ~0x3UL) == PP_SIGNATURE) |
>> -#endif
>> +			page_pool_page_is_pp(page) |
>>  			(page->flags & check_flags)))
>>  		return false;
>>  
>> @@ -926,10 +925,8 @@ static const char *page_bad_reason(struct page *page, unsigned long flags)
>>  	if (unlikely(page->memcg_data))
>>  		bad_reason = "page still charged to cgroup";
>>  #endif
>> -#ifdef CONFIG_PAGE_POOL
>> -	if (unlikely((page->pp_magic & ~0x3UL) == PP_SIGNATURE))
>> +	if (unlikely(page_pool_page_is_pp(page)))
>>  		bad_reason = "page_pool leak";
>> -#endif
>>  	return bad_reason;
>>  }
>>  
>
> I wonder if it is OK to make page allocation depend on page_pool from
> net/page_pool.

Why? It's not really a dependency, just a header include with a static
inline function...

> Would linux/mm.h be a better place for page_pool_page_is_pp()?

That would require moving all the definitions introduced in patch 2,
which I don't think is appropriate.

-Toke