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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> MIME-Version: 1.0 X-Originating-IP: [10.90.30.45] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemf200006.china.huawei.com (7.185.36.61) X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 595D1180029 X-Stat-Signature: qztn6bjyh7juaq8h6wcc9dpsbekfjf5o X-Rspam-User: X-HE-Tag: 1730117100-804095 X-HE-Meta: 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 abLn8ZSy DYWUDycZrcfGvDFQlSIB2BU/QiN7RESKpTJp8DMjxz0BemeSc/JM2vv03e+MQ31o5CR6+0+uyEvIOT6SRRl/ljvnWtlqZ26D1jEmotyMMSMkxFy3OtjgZ4BULOYGvMPtbxofFhFkz//n3wuNwbuAuYydtM8Gneq7rR+P1+9cjnOgczEFTt52MnccE4rkHo5BoVsz3y8kQ9to/lDaxkS59OPwSbUHymbP+jG7KW3u9KKSwrjfB5b1l+OSOAVwhwRR24Vjf1U02zolLgJo2m2UwwEQ2SrsD47DwZJaAqRsBlbcDdIRilQL8ukJqK+GSTyxm1PmxUkXI4ZPRu4JB/KTsRWyALaE6TYpQkcoxwBMUredrPoBFT9pHnRzU/CP7up4pzqnAqKljrQil2nNSC252v71Kzw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 + ============== Page fragments ============== @@ -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. -Alexander Duyck, Nov 29, 2016. + +Architecture overview +===================== + +.. 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 enough + | | | + PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE | | + | | | + | PAGE_SIZE >= PAGE_FRAG_CACHE_MAX_SIZE | + v | | + +----------------------------------+ | | + | refill cache with order > 0 page | | | + +----------------------------------+ | | + | | | | + | | | | + | Refill failed | | + | | | | + | v v | + | +------------------------------------+ | + | | refill cache with order 0 page | | + | +----------------------------------=-+ | + | | | + Refill succeed | | + | Refill succeed | + | | | + v v v + +------------------------------------------------------------------+ + | allocate fragment from cache | + +------------------------------------------------------------------+ + +API interface +============= + +Depending on different aligning requirement, the page_frag API caller may call +page_frag_*_align*() to ensure the returned virtual address or offset of the +page is aligned according to the 'align/alignment' parameter. Note the size of +the allocated fragment is not aligned, the caller needs to provide an aligned +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 +=============== + +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 = page_frag_alloc_align(nc, size, gfp, align); + if (!va) + goto do_error; + + err = 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_cache.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(unsigned long encoded_page) return !!(encoded_page & PAGE_FRAG_CACHE_PFMEMALLOC_BIT); } +/** + * 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 = 0; } +/** + * 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 pfmemalloc + * 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 pfmemalloc + * reserves, otherwise return false. + */ static inline bool page_frag_cache_is_pfmemalloc(struct page_frag_cache *nc) { return encoded_page_decode_pfmemalloc(nc->encoded_page); @@ -57,6 +74,19 @@ static inline unsigned int __page_frag_cache_commit(struct page_frag_cache *nc, return __page_frag_cache_commit_noref(nc, pfrag, used_sz); } +/** + * __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; } +/** + * 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 needs to be refilled + * @align: the requested aligning requirement for the fragment + * + * WARN_ON_ONCE() checking for @align before allocating 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) @@ -80,6 +123,17 @@ static inline void *page_frag_alloc_align(struct page_frag_cache *nc, return __page_frag_alloc_align(nc, fragsz, gfp_mask, -align); } +/** + * 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; } +/** + * 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); -/* - * Frees a page fragment allocated out of either a compound or order 0 page. +/** + * 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) {