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Message-ID: <87v7rgw1us.fsf@toke.dk>
Date: Mon, 07 Apr 2025 15:14:03 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Zi Yan <ziy@...dia.com>
Cc: "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>, 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:
> 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/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.
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.
>
> Why? I do not see page_pool_page_is_pp() or PP_SIGNATURE is used anywhere
> in patch 2.
Look again. Patch 2 redefines PP_MAGIC_MASK in terms of all the other
definitions.
-Toke
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