[net-next,v2,14/15] mm: page_frag: update documentation for page_frag

Message ID	20240415131941.51153-15-linyunsheng@huawei.com (mailing list archive)
State	New
Headers	show Return-Path: <owner-linux-mm@kvack.org> From: Yunsheng Lin <linyunsheng@huawei.com> To: <davem@davemloft.net>, <kuba@kernel.org>, <pabeni@redhat.com> CC: <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>, Yunsheng Lin <linyunsheng@huawei.com>, Alexander Duyck <alexander.duyck@gmail.com>, Jonathan Corbet <corbet@lwn.net>, Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>, <linux-doc@vger.kernel.org> Subject: [PATCH net-next v2 14/15] mm: page_frag: update documentation for page_frag Date: Mon, 15 Apr 2024 21:19:39 +0800 Message-ID: <20240415131941.51153-15-linyunsheng@huawei.com> In-Reply-To: <20240415131941.51153-1-linyunsheng@huawei.com> References: <20240415131941.51153-1-linyunsheng@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset="y" Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Precedence: bulk
Series	[net-next,v2,01/15] mm: page_frag: add a test module for page_frag \| expand [net-next,v2,01/15] mm: page_frag: add a test module for page_frag [net-next,v2,03/15] mm: page_frag: use free_unref_page() to free page fragment [net-next,v2,04/15] mm: move the page fragment allocator from page_alloc into its own file [net-next,v2,05/15] mm: page_frag: use initial zero offset for page_frag_alloc_align() [net-next,v2,06/15] mm: page_frag: change page_frag_alloc_* API to accept align param [net-next,v2,07/15] mm: page_frag: add '_va' suffix to page_frag API [net-next,v2,08/15] mm: page_frag: add two inline helper for page_frag API [net-next,v2,09/15] mm: page_frag: reuse MSB of 'size' field for pfmemalloc [net-next,v2,10/15] mm: page_frag: reuse existing bit field of 'va' for pagecnt_bias [net-next,v2,12/15] mm: page_frag: introduce prepare/commit API for page_frag [net-next,v2,14/15] mm: page_frag: update documentation for page_frag

diff --git a/Documentation/mm/page_frags.rst b/Documentation/mm/page_frags.rst index 503ca6cdb804..ac9dd9e8ee16 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 +42,148 @@ 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 | + | Cache empty v | + | +-----------------+ | + | | drain old cache | | + | +-----------------+ | + | ^ | + | | | + v v | + +----------------------------------+ | + | refill cache with order 3 page | | + +----------------------------------+ | + ^ ^ | + | | | + | | Refill failed | + | | | Cache is enough + | | | + | v | + | +----------------------------------+ | + | | refill cache with order 0 page | | + | +----------------------------------+ | + | ^ | + | Refill succeed | | + | | Refill succeed | + | | | + v v v + +------------------------------------------------+ + | allocate fragment from cache | + +------------------------------------------------+ + +API interface +============= +As the design and implementation of page_frag API, the allocation side does not +allow concurrent calling, it is assumed that the caller must ensure there is not +concurrent alloc calling to the same page_frag_cache instance by using it's own +lock or rely on some lockless guarantee like NAPI softirq. + +Depending on different use cases, callers expecting to deal with va, page or +both va and page for them may call page_frag_alloc_va*, page_frag_alloc_pg*, +or page_frag_alloc* API accordingly. + +There is also a use case that need minimum memory in order for forward +progressing, but can do better if there is more memory available. Introduce +page_frag_alloc_prepare() and page_frag_alloc_commit() related API, the caller +requests the minimum memory it need and the prepare API will return the maximum +size of the fragment returned, caller need to report back to the page_frag core +how much memory it actually use by calling commit API, or not calling the commit +API if deciding to not use any memory. + +.. kernel-doc:: include/linux/page_frag_cache.h + :identifiers: page_frag_cache_init page_frag_cache_is_pfmemalloc + page_frag_alloc_va __page_frag_alloc_va_align + page_frag_alloc_va_align page_frag_alloc_va_prepare + page_frag_alloc_va_prepare_align page_frag_alloc_pg_prepare + page_frag_alloc_prepare page_frag_alloc_commit + page_frag_alloc_commit_noref page_frag_free_va + +.. kernel-doc:: mm/page_frag_cache.c + :identifiers: page_frag_cache_drain + +Coding examples +=============== + +Init & Drain API +---------------- + +.. code-block:: c + + page_frag_cache_init(pfrag); + ... + page_frag_cache_drain(pfrag); + + +Alloc & Free API +---------------- + +.. code-block:: c + + void *va; + + va = page_frag_alloc_va_align(pfrag, size, gfp, align); + if (!va) + goto do_error; + + err = do_something(va, size); + if (err) { + page_frag_free_va(va); + goto do_error; + } + +Prepare & Commit API +-------------------- + +.. code-block:: c + + unsigned int offset, size; + bool merge = true; + struct page *page; + void *va; + + size = 32U; + page = page_frag_alloc_prepare(pfrag, &offset, &size, &va); + if (!page) + goto wait_for_space; + + copy = min_t(int, copy, size); + if (!skb_can_coalesce(skb, i, page, offset)) { + if (i >= max_skb_frags) + goto new_segment; + + merge = false; + } + + copy = mem_schedule(copy); + if (!copy) + goto wait_for_space; + + err = copy_from_iter_full_nocache(va, copy, iter); + if (err) + goto do_error; + + if (merge) { + skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy); + page_frag_alloc_commit_noref(pfrag, offset, copy); + } else { + skb_fill_page_desc(skb, i, page, offset, copy); + page_frag_alloc_commit(pfrag, offset, copy); + } diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cache.h index 28185969cd2c..529e7c040dad 100644 --- a/include/linux/page_frag_cache.h +++ b/include/linux/page_frag_cache.h @@ -31,11 +31,28 @@ struct page_frag_cache { #endif }; +/** + * page_frag_cache_init() - Init page_frag cache. + * @nc: page_frag cache from which to init + * + * Inline helper to init the page_frag cache. + */ static inline void page_frag_cache_init(struct page_frag_cache *nc) { nc->va = NULL; } +/** + * page_frag_cache_is_pfmemalloc() - Check for pfmemalloc. + * @nc: page_frag cache from which to check + * + * Used to check if the current page in page_frag cache is pfmemalloc'ed. + * It has the same calling context expection as the alloc API. + * + * Return: + * Return true if the current page in page_frag cache is pfmemalloc'ed, + * otherwise return false. + */ static inline bool page_frag_cache_is_pfmemalloc(struct page_frag_cache *nc) { return !!nc->pfmemalloc; @@ -46,6 +63,17 @@ void __page_frag_cache_drain(struct page *page, unsigned int count); void *page_frag_cache_refill(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask); +/** + * page_frag_alloc_va() - Alloc 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 + * + * Get a page fragment from page_frag cache. + * + * Return: + * Return va of the page fragment, otherwise return NULL. + */ static inline void *page_frag_alloc_va(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask) { @@ -63,6 +91,19 @@ static inline void *page_frag_alloc_va(struct page_frag_cache *nc, return va + offset; } +/** + * __page_frag_alloc_va_align() - Alloc 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: the requested aligning requirement + * + * Get a page fragment from page_frag cache with aligning requirement. + * + * Return: + * Return va of the page fragment, otherwise return NULL. + */ static inline void *__page_frag_alloc_va_align(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask, @@ -75,6 +116,19 @@ static inline void *__page_frag_alloc_va_align(struct page_frag_cache *nc, return page_frag_alloc_va(nc, fragsz, gfp_mask); } +/** + * page_frag_alloc_va_align() - Alloc 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: the requested aligning requirement + * + * WARN_ON_ONCE() checking for align and fragsz before getting a page fragment + * from page_frag cache with aligning requirement. + * + * Return: + * Return va of the page fragment, otherwise return NULL. + */ static inline void *page_frag_alloc_va_align(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask, @@ -86,6 +140,19 @@ static inline void *page_frag_alloc_va_align(struct page_frag_cache *nc, return __page_frag_alloc_va_align(nc, fragsz, gfp_mask, align); } +/** + * page_frag_alloc_va_prepare() - Prepare allocing a page fragment. + * @nc: page_frag cache from which to prepare + * @offset: out as the offset of the page fragment + * @size: in as the requested size, out as the available size + * @gfp_mask: the allocation gfp to use when cache need to be refilled + * + * Prepare a page fragment with minimum size of ‘size’, 'size' is also used to + * report the maximum size of the page fragment the caller can use. + * + * Return: + * Return va of the page fragment, otherwise return NULL. + */ static inline void *page_frag_alloc_va_prepare(struct page_frag_cache *nc, unsigned int *offset, unsigned int *size, @@ -108,6 +175,21 @@ static inline void *page_frag_alloc_va_prepare(struct page_frag_cache *nc, return va + *offset; } +/** + * page_frag_alloc_va_prepare_align() - Prepare allocing a page fragment with + * aligning requirement. + * @nc: page_frag cache from which to prepare + * @offset: out as the offset of the page fragment + * @size: in as the requested size, out as the available size + * @align: the requested aligning requirement + * @gfp_mask: the allocation gfp to use when cache need to be refilled + * + * Prepare an aligned page fragment with minimum size of ‘size’, 'size' is also + * used to report the maximum size of the page fragment the caller can use. + * + * Return: + * Return va of the page fragment, otherwise return NULL. + */ static inline void *page_frag_alloc_va_prepare_align(struct page_frag_cache *nc, unsigned int *offset, unsigned int *size, @@ -144,6 +226,19 @@ static inline void *__page_frag_alloc_pg_prepare(struct page_frag_cache *nc, return va; } +/** + * page_frag_alloc_pg_prepare - Prepare allocing a page fragment. + * @nc: page_frag cache from which to prepare + * @offset: out as the offset of the page fragment + * @size: in as the requested size, out as the available size + * @gfp: the allocation gfp to use when cache need to be refilled + * + * Prepare a page fragment with minimum size of ‘size’, 'size' is also used to + * report the maximum size of the page fragment the caller can use. + * + * Return: + * Return the page fragment, otherwise return NULL. + */ #define page_frag_alloc_pg_prepare(nc, offset, size, gfp) \ ({ \ struct page *__page = NULL; \ @@ -179,6 +274,21 @@ static inline void *__page_frag_alloc_prepare(struct page_frag_cache *nc, return nc_va; } +/** + * page_frag_alloc_prepare - Prepare allocing a page fragment. + * @nc: page_frag cache from which to prepare + * @offset: out as the offset of the page fragment + * @size: in as the requested size, out as the available size + * @va: out as the va of the returned page fragment + * @gfp: the allocation gfp to use when cache need to be refilled + * + * Prepare a page fragment with minimum size of ‘size’, 'size' is also used to + * report the maximum size of the page fragment. Return both 'page' and 'va' of + * the fragment to the caller. + * + * Return: + * Return the page fragment, otherwise return NULL. + */ #define page_frag_alloc_prepare(nc, offset, size, va, gfp) \ ({ \ struct page *__page = NULL; \ @@ -191,6 +301,14 @@ static inline void *__page_frag_alloc_prepare(struct page_frag_cache *nc, __page; \ }) +/** + * page_frag_alloc_commit - Commit allocing a page fragment. + * @nc: page_frag cache from which to commit + * @offset: offset of the page fragment + * @size: size of the page fragment has been used + * + * Commit the alloc preparing by passing offset and the actual used size. + */ static inline void page_frag_alloc_commit(struct page_frag_cache *nc, unsigned int offset, unsigned int size) @@ -199,6 +317,17 @@ static inline void page_frag_alloc_commit(struct page_frag_cache *nc, nc->offset = offset + size; } +/** + * page_frag_alloc_commit_noref - Commit allocing a page fragment without taking + * page refcount. + * @nc: page_frag cache from which to commit + * @offset: offset of the page fragment + * @size: size of the page fragment has been used + * + * Commit the alloc preparing by passing offset and the actual used size, but + * not taking page refcount. Mostly used for fragmemt coaleasing case when the + * current fragmemt can share the same refcount with previous fragmemt. + */ static inline void page_frag_alloc_commit_noref(struct page_frag_cache *nc, unsigned int offset, unsigned int size) @@ -206,6 +335,10 @@ static inline void page_frag_alloc_commit_noref(struct page_frag_cache *nc, nc->offset = offset + size; } +/** + * page_frag_free_va - Free a page fragment by va. + * @addr: va of page fragment to be freed + */ void page_frag_free_va(void *addr); #endif diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c index 8774cb07e630..8b1d35aafcc1 100644 --- a/mm/page_frag_cache.c +++ b/mm/page_frag_cache.c @@ -60,6 +60,10 @@ static bool __page_frag_cache_refill(struct page_frag_cache *nc, return true; } +/** + * 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->va)

[net-next,v2,14/15] mm: page_frag: update documentation for page_frag

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