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Date: Thu, 23 Sep 2021 19:24:24 +0800 From: Yunsheng Lin <linyunsheng@...wei.com> To: Ilias Apalodimas <ilias.apalodimas@...aro.org> CC: <davem@...emloft.net>, <kuba@...nel.org>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <linuxarm@...neuler.org>, <hawk@...nel.org>, <jonathan.lemon@...il.com>, <alobakin@...me>, <willemb@...gle.com>, <cong.wang@...edance.com>, <pabeni@...hat.com>, <haokexin@...il.com>, <nogikh@...gle.com>, <elver@...gle.com>, <memxor@...il.com>, <edumazet@...gle.com>, <alexander.duyck@...il.com>, <dsahern@...il.com> Subject: Re: [PATCH net-next 3/7] pool_pool: avoid calling compound_head() for skb frag page On 2021/9/23 16:33, Ilias Apalodimas wrote: > On Wed, Sep 22, 2021 at 05:41:27PM +0800, Yunsheng Lin wrote: >> As the pp page for a skb frag is always a head page, so make >> sure skb_pp_recycle() passes a head page to avoid calling >> compound_head() for skb frag page case. > > Doesn't that rely on the driver mostly (i.e what's passed in skb_frag_set_page() ? > None of the current netstack code assumes bv_page is the head page of a > compound page. Since our page_pool allocator can will allocate compound > pages for order > 0, why should we rely on it ? As the page pool alloc function return 'struct page *' to the caller, which is the head page of a compound pages for order > 0, so I assume the caller will pass that to skb_frag_set_page(). For non-pp page, I assume it is ok whether the page is a head page or tail page, as the pp_magic for both of them are not set with PP_SIGNATURE. Or should we play safe here, and do the trick as skb_free_head() does in patch 6? > > Thanks > /Ilias >> >> Signed-off-by: Yunsheng Lin <linyunsheng@...wei.com> >> --- >> include/linux/skbuff.h | 2 +- >> net/core/page_pool.c | 2 -- >> 2 files changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h >> index 6bdb0db3e825..35eebc2310a5 100644 >> --- a/include/linux/skbuff.h >> +++ b/include/linux/skbuff.h >> @@ -4722,7 +4722,7 @@ static inline bool skb_pp_recycle(struct sk_buff *skb, void *data) >> { >> if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle) >> return false; >> - return page_pool_return_skb_page(virt_to_page(data)); >> + return page_pool_return_skb_page(virt_to_head_page(data)); >> } >> >> #endif /* __KERNEL__ */ >> diff --git a/net/core/page_pool.c b/net/core/page_pool.c >> index f7e71dcb6a2e..357fb53343a0 100644 >> --- a/net/core/page_pool.c >> +++ b/net/core/page_pool.c >> @@ -742,8 +742,6 @@ bool page_pool_return_skb_page(struct page *page) >> { >> struct page_pool *pp; >> >> - page = compound_head(page); >> - >> /* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation >> * in order to preserve any existing bits, such as bit 0 for the >> * head page of compound page and bit 1 for pfmemalloc page, so >> -- >> 2.33.0 >> > . >
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