From nobody Mon Nov 25 11:17:57 2024 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4E77D1D934D; Mon, 28 Oct 2024 12:05:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.188 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730117119; cv=none; b=Zaidiw4DNmxYu72Och+Hhjhuasc+u5qzioWp6Fz0nSoPDA5zR0bckzz9j9oFEsMCNAvK/i1qqunA+vTo/5cpQnv/IC1xoJWx6MbNOFCG5j0kmanHMFxEKPwUucGtu1O8+KCQ642wOn/HwH8hf3f/UD8q48O/wyAQNpZIPtIg7z4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730117119; c=relaxed/simple; bh=AnS873QB+hwd0VrFLf/D5rY6qh3rve2wNTTBNEyvE14=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=HjdhPq/FUVbvmtirnCczVW1JYteFKAQp59Unf549dOaDmbbMGo7Pce9KIqH+L098vxoViN2r69ewJJyCq7EDmrYR8S+8iqAsafYKfPSfzsb1Le81xCTcbsQ85syzdDpO+pEIxzHy7Vzejhu2Oqvs+P5KzcJOnGBhbYBBScTCapM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.174]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4XcX8108CfzfdT3; Mon, 28 Oct 2024 20:02:41 +0800 (CST) Received: from dggpemf200006.china.huawei.com (unknown [7.185.36.61]) by mail.maildlp.com (Postfix) with ESMTPS id B429C1402CC; Mon, 28 Oct 2024 20:05:13 +0800 (CST) Received: from localhost.localdomain (10.90.30.45) by dggpemf200006.china.huawei.com (7.185.36.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 28 Oct 2024 20:05:13 +0800 From: Yunsheng Lin To: , , CC: , , Yunsheng Lin , Alexander Duyck , Andrew Morton , Linux-MM , Jonathan Corbet , Subject: [PATCH RFC 03/10] mm: page_frag: update documentation for page_frag Date: Mon, 28 Oct 2024 19:58:43 +0800 Message-ID: <20241028115850.3409893-4-linyunsheng@huawei.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20241028115850.3409893-1-linyunsheng@huawei.com> References: <20241028115850.3409893-1-linyunsheng@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemf200006.china.huawei.com (7.185.36.61) Content-Type: text/plain; charset="utf-8" Update documentation about design, implementation and API usages for page_frag. CC: Alexander Duyck CC: Andrew Morton CC: Linux-MM Signed-off-by: Yunsheng Lin --- Documentation/mm/page_frags.rst | 110 +++++++++++++++++++++++++++++++- include/linux/page_frag_cache.h | 54 ++++++++++++++++ mm/page_frag_cache.c | 12 +++- 3 files changed, 173 insertions(+), 3 deletions(-) diff --git a/Documentation/mm/page_frags.rst b/Documentation/mm/page_frags.= rst index 503ca6cdb804..34e654c2956e 100644 --- a/Documentation/mm/page_frags.rst +++ b/Documentation/mm/page_frags.rst @@ -1,3 +1,5 @@ +.. SPDX-License-Identifier: GPL-2.0 + =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Page fragments =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D @@ -40,4 +42,110 @@ page via a single call. The advantage to doing this is= that it allows for cleaning up the multiple references that were added to a page in order to avoid calling get_page per allocation. =20 -Alexander Duyck, Nov 29, 2016. + +Architecture overview +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +.. code-block:: none + + +----------------------+ + | page_frag API caller | + +----------------------+ + | + | + v + +------------------------------------------------------------------+ + | request page fragment | + +------------------------------------------------------------------+ + | | | + | | | + | Cache not enough | + | | | + | +-----------------+ | + | | reuse old cache |--Usable-->| + | +-----------------+ | + | | | + | Not usable | + | | | + | v | + Cache empty +-----------------+ | + | | drain old cache | | + | +-----------------+ | + | | | + v_________________________________v | + | | + | | + _________________v_______________ | + | | Cache is enou= gh + | | | + PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE | | + | | | + | PAGE_SIZE >=3D PAGE_FRAG_CACHE_MAX_SIZE | + v | | + +----------------------------------+ | | + | refill cache with order > 0 page | | | + +----------------------------------+ | | + | | | | + | | | | + | Refill failed | | + | | | | + | v v | + | +------------------------------------+ | + | | refill cache with order 0 page | | + | +----------------------------------=3D-+ | + | | | + Refill succeed | | + | Refill succeed | + | | | + v v v + +------------------------------------------------------------------+ + | allocate fragment from cache | + +------------------------------------------------------------------+ + +API interface +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Depending on different aligning requirement, the page_frag API caller may = call +page_frag_*_align*() to ensure the returned virtual address or offset of t= he +page is aligned according to the 'align/alignment' parameter. Note the siz= e of +the allocated fragment is not aligned, the caller needs to provide an alig= ned +fragsz if there is an alignment requirement for the size of the fragment. + +.. kernel-doc:: include/linux/page_frag_cache.h + :identifiers: page_frag_cache_init page_frag_cache_is_pfmemalloc + __page_frag_alloc_align page_frag_alloc_align page_frag_alloc + +.. kernel-doc:: mm/page_frag_cache.c + :identifiers: page_frag_cache_drain page_frag_free + +Coding examples +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +Initialization and draining API +------------------------------- + +.. code-block:: c + + page_frag_cache_init(nc); + ... + page_frag_cache_drain(nc); + + +Allocation & freeing API +------------------------ + +.. code-block:: c + + void *va; + + va =3D page_frag_alloc_align(nc, size, gfp, align); + if (!va) + goto do_error; + + err =3D do_something(va, size); + if (err) + goto do_error; + + ... + + page_frag_free(va); diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cach= e.h index 5ae97f93a0a1..a2b1127e8ac8 100644 --- a/include/linux/page_frag_cache.h +++ b/include/linux/page_frag_cache.h @@ -28,11 +28,28 @@ static inline bool encoded_page_decode_pfmemalloc(unsig= ned long encoded_page) return !!(encoded_page & PAGE_FRAG_CACHE_PFMEMALLOC_BIT); } =20 +/** + * page_frag_cache_init() - Init page_frag cache. + * @nc: page_frag cache from which to init + * + * Inline helper to initialize the page_frag cache. + */ static inline void page_frag_cache_init(struct page_frag_cache *nc) { nc->encoded_page =3D 0; } =20 +/** + * page_frag_cache_is_pfmemalloc() - Check for pfmemalloc. + * @nc: page_frag cache from which to check + * + * Check if the current page in page_frag cache is allocated from the pfme= malloc + * reserves. It has the same calling context expectation as the allocation= API. + * + * Return: + * true if the current page in page_frag cache is allocated from the pfmem= alloc + * reserves, otherwise return false. + */ static inline bool page_frag_cache_is_pfmemalloc(struct page_frag_cache *n= c) { return encoded_page_decode_pfmemalloc(nc->encoded_page); @@ -57,6 +74,19 @@ static inline unsigned int __page_frag_cache_commit(stru= ct page_frag_cache *nc, return __page_frag_cache_commit_noref(nc, pfrag, used_sz); } =20 +/** + * __page_frag_alloc_align() - Allocate a page fragment with aligning + * requirement. + * @nc: page_frag cache from which to allocate + * @fragsz: the requested fragment size + * @gfp_mask: the allocation gfp to use when cache need to be refilled + * @align_mask: the requested aligning requirement for the 'va' + * + * Allocate a page fragment from page_frag cache with aligning requirement. + * + * Return: + * Virtual address of the page fragment, otherwise return NULL. + */ static inline void *__page_frag_alloc_align(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask, unsigned int align_mask) @@ -72,6 +102,19 @@ static inline void *__page_frag_alloc_align(struct page= _frag_cache *nc, return va; } =20 +/** + * page_frag_alloc_align() - Allocate a page fragment with aligning requir= ement. + * @nc: page_frag cache from which to allocate + * @fragsz: the requested fragment size + * @gfp_mask: the allocation gfp to use when cache needs to be refilled + * @align: the requested aligning requirement for the fragment + * + * WARN_ON_ONCE() checking for @align before allocating a page fragment fr= om + * page_frag cache with aligning requirement. + * + * Return: + * virtual address of the page fragment, otherwise return NULL. + */ static inline void *page_frag_alloc_align(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask, unsigned int align) @@ -80,6 +123,17 @@ static inline void *page_frag_alloc_align(struct page_f= rag_cache *nc, return __page_frag_alloc_align(nc, fragsz, gfp_mask, -align); } =20 +/** + * page_frag_alloc() - Allocate a page fragment. + * @nc: page_frag cache from which to allocate + * @fragsz: the requested fragment size + * @gfp_mask: the allocation gfp to use when cache need to be refilled + * + * Allocate a page fragment from page_frag cache. + * + * Return: + * virtual address of the page fragment, otherwise return NULL. + */ static inline void *page_frag_alloc(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask) { diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c index f55d34cf7d43..d014130fb893 100644 --- a/mm/page_frag_cache.c +++ b/mm/page_frag_cache.c @@ -70,6 +70,10 @@ static struct page *__page_frag_cache_refill(struct page= _frag_cache *nc, return page; } =20 +/** + * page_frag_cache_drain - Drain the current page from page_frag cache. + * @nc: page_frag cache from which to drain + */ void page_frag_cache_drain(struct page_frag_cache *nc) { if (!nc->encoded_page) @@ -182,8 +186,12 @@ void *__page_frag_cache_prepare(struct page_frag_cache= *nc, unsigned int fragsz, } EXPORT_SYMBOL(__page_frag_cache_prepare); =20 -/* - * Frees a page fragment allocated out of either a compound or order 0 pag= e. +/** + * page_frag_free - Free a page fragment. + * @addr: va of page fragment to be freed + * + * Free a page fragment allocated out of either a compound or order 0 page= by + * virtual address. */ void page_frag_free(void *addr) { --=20 2.33.0