From patchwork Thu Nov 23 02:25:14 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Liang Chen X-Patchwork-Id: 13465696 X-Patchwork-Delegate: kuba@kernel.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Fzp/kCoy" Received: from mail-pl1-x62a.google.com (mail-pl1-x62a.google.com [IPv6:2607:f8b0:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C2461A8 for ; Wed, 22 Nov 2023 18:25:40 -0800 (PST) Received: by mail-pl1-x62a.google.com with SMTP id d9443c01a7336-1cf61eed213so3393505ad.2 for ; Wed, 22 Nov 2023 18:25:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1700706339; x=1701311139; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=alCRNwrrdh7rHKNUzjSmzrgdnxE0eijK4L857D75ssc=; b=Fzp/kCoynNdmKi/Rs4yMPoBlJrXUaLmVQ6MNuwBvynyvTePlXiTWsrVy6gAFyCCp08 OFwqq9IZFGXRahqzd6F2QUvFvgr0leeerzdUQhAdS8Vpq4emWCZbBVQf2BGbDjnCKgG4 NrIa4AAJTqcNlQ6/H7/eonQ+icaIanrfcRL1Pp2GRSo46cuQJR/5B8DSKcYo1J/Oy6pm XZV0Ld/T1Eq+eGxdB6Sotehg2JqqQ1Me0bzcr6zZEbntwpdvn8k+eHOlVDIwUXcNQHJf i7C/1pkrl+rJLhgeI3Fmhi0TzHjEDpshzlkrZXVLSrXoxYEvv650iYjU4nwmGPo87Nk/ 2JZg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1700706339; x=1701311139; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=alCRNwrrdh7rHKNUzjSmzrgdnxE0eijK4L857D75ssc=; b=gF7QnBQb4W4Dnroc7zxk0mQRLs9waUMOSfIalNvaRrymIodN/vJkFoA3nYRdP+zeL4 Ze9uDWquEutGktsAQzPDrsDs2ZRVqyaul7GzzE48HsSHlR5POiPohvO5+bWRJDysb4td 1hVmka9SaSHVeY5omaiWNg4tkgHMaBPdO5uxHCBvUDDnboUoOXK8iz3P+5FYRiCU/QlD CSdY9HUIfZGcFIEsdVbSKAipGfohsiCiZg3X1d/2cTlnjqE0YAqWoj3H2bn7pVkp2BnR Lg0lu9qA/607xHJ4SP0+Ht/bSxwwhgcoBp4OGJvxFMymbsZBrIJhx7i+SDdzXfz6ScK0 mgUA== X-Gm-Message-State: AOJu0YyU1i0mMtZzDmmfubAu+aMG/p7ZKi1UiZ3v8hYPnTNdgKr1JBvF Odxh0dxLApyfi/yalAEI0Mg= X-Google-Smtp-Source: AGHT+IEG52qjzrUeruPSojmlN7ETuyzZbhdWyD2gZBEzpIbw7WjFTO6cPT+hHLaRHL7XjIPh8c6egw== X-Received: by 2002:a17:902:9044:b0:1cc:29ed:96ae with SMTP id w4-20020a170902904400b001cc29ed96aemr4162097plz.41.1700706339368; Wed, 22 Nov 2023 18:25:39 -0800 (PST) Received: from localhost.localdomain ([204.44.110.111]) by smtp.gmail.com with ESMTPSA id v11-20020a170902d68b00b001ce6452a741sm32880ply.25.2023.11.22.18.25.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Nov 2023 18:25:38 -0800 (PST) From: Liang Chen To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, hawk@kernel.org, ilias.apalodimas@linaro.org, linyunsheng@huawei.com Cc: netdev@vger.kernel.org, linux-mm@kvack.org, liangchen.linux@gmail.com Subject: [PATCH net-next v2 1/3] page_pool: Rename pp_frag_count to pp_ref_count Date: Thu, 23 Nov 2023 10:25:14 +0800 Message-Id: <20231123022516.6757-1-liangchen.linux@gmail.com> X-Mailer: git-send-email 2.31.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org To support multiple users referencing the same fragment, pp_frag_count is renamed to pp_ref_count to better reflect its actual meaning based on the suggestion from [1]. [1] http://lore.kernel.org/netdev/f71d9448-70c8-8793-dc9a-0eb48a570300@huawei.com Signed-off-by: Liang Chen --- include/linux/mm_types.h | 2 +- include/net/page_pool/helpers.h | 31 ++++++++++++++++++------------- 2 files changed, 19 insertions(+), 14 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 957ce38768b2..64e4572ef06d 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -125,7 +125,7 @@ struct page { struct page_pool *pp; unsigned long _pp_mapping_pad; unsigned long dma_addr; - atomic_long_t pp_frag_count; + atomic_long_t pp_ref_count; }; struct { /* Tail pages of compound page */ unsigned long compound_head; /* Bit zero is set */ diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h index 4ebd544ae977..a6dc9412c9ae 100644 --- a/include/net/page_pool/helpers.h +++ b/include/net/page_pool/helpers.h @@ -29,7 +29,7 @@ * page allocated from page pool. Page splitting enables memory saving and thus * avoids TLB/cache miss for data access, but there also is some cost to * implement page splitting, mainly some cache line dirtying/bouncing for - * 'struct page' and atomic operation for page->pp_frag_count. + * 'struct page' and atomic operation for page->pp_ref_count. * * The API keeps track of in-flight pages, in order to let API users know when * it is safe to free a page_pool object, the API users must call @@ -214,61 +214,66 @@ inline enum dma_data_direction page_pool_get_dma_dir(struct page_pool *pool) return pool->p.dma_dir; } -/* pp_frag_count represents the number of writers who can update the page +/* pp_ref_count represents the number of writers who can update the page * either by updating skb->data or via DMA mappings for the device. * We can't rely on the page refcnt for that as we don't know who might be * holding page references and we can't reliably destroy or sync DMA mappings * of the fragments. * - * When pp_frag_count reaches 0 we can either recycle the page if the page + * pp_ref_count initially corresponds to the number of fragments. However, + * when multiple users start to reference a single fragment, for example in + * skb_try_coalesce, the pp_ref_count will become greater than the number of + * fragments. + * + * When pp_ref_count reaches 0 we can either recycle the page if the page * refcnt is 1 or return it back to the memory allocator and destroy any * mappings we have. */ static inline void page_pool_fragment_page(struct page *page, long nr) { - atomic_long_set(&page->pp_frag_count, nr); + atomic_long_set(&page->pp_ref_count, nr); } static inline long page_pool_defrag_page(struct page *page, long nr) { long ret; - /* If nr == pp_frag_count then we have cleared all remaining + /* If nr == pp_ref_count then we have cleared all remaining * references to the page: * 1. 'n == 1': no need to actually overwrite it. * 2. 'n != 1': overwrite it with one, which is the rare case - * for pp_frag_count draining. + * for pp_ref_count draining. * * The main advantage to doing this is that not only we avoid a atomic * update, as an atomic_read is generally a much cheaper operation than * an atomic update, especially when dealing with a page that may be - * partitioned into only 2 or 3 pieces; but also unify the pp_frag_count + * partitioned into only 2 or 3 pieces; but also unify the pp_ref_count * handling by ensuring all pages have partitioned into only 1 piece * initially, and only overwrite it when the page is partitioned into * more than one piece. */ - if (atomic_long_read(&page->pp_frag_count) == nr) { + if (atomic_long_read(&page->pp_ref_count) == nr) { /* As we have ensured nr is always one for constant case using * the BUILD_BUG_ON(), only need to handle the non-constant case - * here for pp_frag_count draining, which is a rare case. + * here for pp_ref_count draining, which is a rare case. */ BUILD_BUG_ON(__builtin_constant_p(nr) && nr != 1); if (!__builtin_constant_p(nr)) - atomic_long_set(&page->pp_frag_count, 1); + atomic_long_set(&page->pp_ref_count, 1); return 0; } - ret = atomic_long_sub_return(nr, &page->pp_frag_count); + ret = atomic_long_sub_return(nr, &page->pp_ref_count); WARN_ON(ret < 0); - /* We are the last user here too, reset pp_frag_count back to 1 to + /* We are the last user here too, reset pp_ref_count back to 1 to * ensure all pages have been partitioned into 1 piece initially, * this should be the rare case when the last two fragment users call * page_pool_defrag_page() currently. */ if (unlikely(!ret)) - atomic_long_set(&page->pp_frag_count, 1); + atomic_long_set(&page->pp_ref_count, 1); return ret; }