Re: [PATCH net-next v7 1/2] page_pool: Move pp_magic check into helper functions

[Zi Yan <ziy@nvidia.com>]

--
Best Regards,
Yan, Zi

On 7 Apr 2025, at 4:53, Toke Høiland-Jørgensen wrote:

> "Zi Yan" <ziy@nvidia.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@google.com>
>>> Tested-by: Yonglong Liu <liuyonglong@huawei.com>
>>> Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
>>> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>>> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.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...

The function is checking, not even modifying, an core mm data structure,
struct page, which is also used by almost all subsystems. I do not get
why the function is in net subsystem.

>
>> 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.

Why? I do not see page_pool_page_is_pp() or PP_SIGNATURE is used anywhere
in patch 2.