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Message-ID: <4d35bda2-d032-49db-bb6e-b1d70f10d436@kernel.org> Date: Mon, 7 Apr 2025 16:43:50 +0200 From: Jesper Dangaard Brouer <hawk@...nel.org> To: Zi Yan <ziy@...dia.com>, Toke Høiland-Jørgensen <toke@...hat.com> 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 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. >>>> 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. >> OK. Just checked. Yes, the function depends on PP_MAGIC_MASK. >> >> But net/types.h has a lot of unrelated page_pool functions and data structures >> mm/page_alloc.c does not care about. Is there a way of moving page_pool_page_is_pp() >> and its dependency to a separate header and including that in mm/page_alloc.c? >> >> Looking at the use of page_pool_page_is_pp() in mm/page_alloc.c, it seems to be >> just error checking. Why can't page_pool do the error checking? > > Or just remove page_pool_page_is_pp() in mm/page_alloc.c. Has it really been used? We have actually used this at Cloudflare to catch some page_pool bugs. And this have been backported to our 6.1 and 6.6 kernels and we have enabled needed config CONFIG_DEBUG_VM (which we measured have low enough overhead to enable in production). AFAIK this is also enabled for our 6.12 kernels. --Jesper
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