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

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Message-ID: <87plhovtx8.fsf@toke.dk>
Date: Mon, 07 Apr 2025 18:05:23 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Zi Yan <ziy@...dia.com>, Jesper Dangaard Brouer <hawk@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...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>,
 netdev@...r.kernel.org, bpf@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-mm@...ck.org, kernel-team <kernel-team@...udflare.com>
Subject: Re: [PATCH net-next v7 1/2] page_pool: Move pp_magic check into
 helper functions

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

> On 7 Apr 2025, at 10:43, Jesper Dangaard Brouer wrote:
>
>> On 07/04/2025 16.15, Zi Yan wrote:
>>> On 7 Apr 2025, at 9:36, Zi Yan wrote:
>>>
>>>> On 7 Apr 2025, at 9:14, Toke Høiland-Jørgensen wrote:
>>>>
>>>>> Zi Yan<ziy@...dia.com>  writes:
>>>>>
>>>>>> Resend to fix my signature.
>>>>>>
>>>>>> On 7 Apr 2025, at 4:53, Toke Høiland-Jørgensen wrote:
>>>>>>
>>>>>>> "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/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.
>>>>> Well, because it's using details of the PP definitions, so keeping it
>>>>> there nicely encapsulates things. I mean, that's the whole point of
>>>>> defining a wrapper function - encapsulating the logic 🙂
>>>>>
>>>>>>>> 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.
>
> The patch at the bottom moves page_pool_page_is_pp() to mm.h and compiles.
> The macros and the function use mm’s page->pp_magic, so I am not sure
> why it is appropriate, especially the user of the macros, net/core/page_pool.c,
> has already included mm.h.

Well, I kinda considered those details page_pool-internal. But okay, I
can move them if you prefer to have them in mm.h.

-Toke