[PATCH net-next v20 10/14] mm: page_frag: introduce prepare/probe/commit API

[Yunsheng Lin]

There are many use cases that need minimum memory in order
for forward progress, but more performant if more memory is
available or need to probe the cache info to use any memory
available for frag caoleasing reason.

Currently skb_page_frag_refill() API is used to solve the
above use cases, but caller needs to know about the internal
detail and access the data field of 'struct page_frag' to
meet the requirement of the above use cases and its
implementation is similar to the one in mm subsystem.

To unify those two page_frag implementations, introduce a
prepare API to ensure minimum memory is satisfied and return
how much the actual memory is available to the caller and a
probe API to report the current available memory to caller
without doing cache refilling. The caller needs to either call
the commit API to report how much memory it actually uses, or
not do so if deciding to not use any memory.

CC: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
---
 include/linux/page_frag_cache.h | 135 ++++++++++++++++++++++++++++++++
 mm/page_frag_cache.c            |  21 +++++
 2 files changed, 156 insertions(+)

diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cache.h
index a6cb32b1d1ca..d91ad53f25d3 100644
--- a/include/linux/page_frag_cache.h
+++ b/include/linux/page_frag_cache.h
@@ -38,6 +38,11 @@ static inline bool page_frag_cache_is_pfmemalloc(struct page_frag_cache *nc)
 	return page_frag_encoded_page_pfmemalloc(nc->encoded_page);
 }
 
+static inline unsigned int page_frag_cache_page_offset(const struct page_frag_cache *nc)
+{
+	return nc->offset;
+}
+
 void page_frag_cache_drain(struct page_frag_cache *nc);
 void __page_frag_cache_drain(struct page *page, unsigned int count);
 void *__page_frag_cache_prepare(struct page_frag_cache *nc, unsigned int fragsz,
@@ -46,6 +51,10 @@ void *__page_frag_cache_prepare(struct page_frag_cache *nc, unsigned int fragsz,
 unsigned int __page_frag_cache_commit_noref(struct page_frag_cache *nc,
 					    struct page_frag *pfrag,
 					    unsigned int used_sz);
+void *__page_frag_alloc_refill_probe_align(struct page_frag_cache *nc,
+					   unsigned int fragsz,
+					   struct page_frag *pfrag,
+					   unsigned int align_mask);
 
 static inline unsigned int __page_frag_cache_commit(struct page_frag_cache *nc,
 						    struct page_frag *pfrag,
@@ -88,6 +97,132 @@ static inline void *page_frag_alloc(struct page_frag_cache *nc,
 	return __page_frag_alloc_align(nc, fragsz, gfp_mask, ~0u);
 }
 
+static inline bool __page_frag_refill_align(struct page_frag_cache *nc,
+					    unsigned int fragsz,
+					    struct page_frag *pfrag,
+					    gfp_t gfp_mask,
+					    unsigned int align_mask)
+{
+	if (unlikely(!__page_frag_cache_prepare(nc, fragsz, pfrag, gfp_mask,
+						align_mask)))
+		return false;
+
+	__page_frag_cache_commit(nc, pfrag, fragsz);
+	return true;
+}
+
+static inline bool page_frag_refill_align(struct page_frag_cache *nc,
+					  unsigned int fragsz,
+					  struct page_frag *pfrag,
+					  gfp_t gfp_mask, unsigned int align)
+{
+	WARN_ON_ONCE(!is_power_of_2(align));
+	return __page_frag_refill_align(nc, fragsz, pfrag, gfp_mask, -align);
+}
+
+static inline bool page_frag_refill(struct page_frag_cache *nc,
+				    unsigned int fragsz,
+				    struct page_frag *pfrag, gfp_t gfp_mask)
+{
+	return __page_frag_refill_align(nc, fragsz, pfrag, gfp_mask, ~0u);
+}
+
+static inline bool __page_frag_refill_prepare_align(struct page_frag_cache *nc,
+						    unsigned int fragsz,
+						    struct page_frag *pfrag,
+						    gfp_t gfp_mask,
+						    unsigned int align_mask)
+{
+	return !!__page_frag_cache_prepare(nc, fragsz, pfrag, gfp_mask,
+					   align_mask);
+}
+
+static inline bool page_frag_refill_prepare_align(struct page_frag_cache *nc,
+						  unsigned int fragsz,
+						  struct page_frag *pfrag,
+						  gfp_t gfp_mask,
+						  unsigned int align)
+{
+	WARN_ON_ONCE(!is_power_of_2(align));
+	return __page_frag_refill_prepare_align(nc, fragsz, pfrag, gfp_mask,
+						-align);
+}
+
+static inline bool page_frag_refill_prepare(struct page_frag_cache *nc,
+					    unsigned int fragsz,
+					    struct page_frag *pfrag,
+					    gfp_t gfp_mask)
+{
+	return __page_frag_refill_prepare_align(nc, fragsz, pfrag, gfp_mask,
+						~0u);
+}
+
+static inline void *__page_frag_alloc_refill_prepare_align(struct page_frag_cache *nc,
+							   unsigned int fragsz,
+							   struct page_frag *pfrag,
+							   gfp_t gfp_mask,
+							   unsigned int align_mask)
+{
+	return __page_frag_cache_prepare(nc, fragsz, pfrag, gfp_mask, align_mask);
+}
+
+static inline void *page_frag_alloc_refill_prepare_align(struct page_frag_cache *nc,
+							 unsigned int fragsz,
+							 struct page_frag *pfrag,
+							 gfp_t gfp_mask,
+							 unsigned int align)
+{
+	WARN_ON_ONCE(!is_power_of_2(align));
+	return __page_frag_alloc_refill_prepare_align(nc, fragsz, pfrag,
+						      gfp_mask, -align);
+}
+
+static inline void *page_frag_alloc_refill_prepare(struct page_frag_cache *nc,
+						   unsigned int fragsz,
+						   struct page_frag *pfrag,
+						   gfp_t gfp_mask)
+{
+	return __page_frag_alloc_refill_prepare_align(nc, fragsz, pfrag,
+						      gfp_mask, ~0u);
+}
+
+static inline void *page_frag_alloc_refill_probe(struct page_frag_cache *nc,
+						 unsigned int fragsz,
+						 struct page_frag *pfrag)
+{
+	return __page_frag_alloc_refill_probe_align(nc, fragsz, pfrag, ~0u);
+}
+
+static inline bool page_frag_refill_probe(struct page_frag_cache *nc,
+					  unsigned int fragsz,
+					  struct page_frag *pfrag)
+{
+	return !!page_frag_alloc_refill_probe(nc, fragsz, pfrag);
+}
+
+static inline void page_frag_commit(struct page_frag_cache *nc,
+				    struct page_frag *pfrag,
+				    unsigned int used_sz)
+{
+	__page_frag_cache_commit(nc, pfrag, used_sz);
+}
+
+static inline void page_frag_commit_noref(struct page_frag_cache *nc,
+					  struct page_frag *pfrag,
+					  unsigned int used_sz)
+{
+	__page_frag_cache_commit_noref(nc, pfrag, used_sz);
+}
+
+static inline void page_frag_alloc_abort(struct page_frag_cache *nc,
+					 unsigned int fragsz)
+{
+	VM_BUG_ON(fragsz > nc->offset);
+
+	nc->pagecnt_bias++;
+	nc->offset -= fragsz;
+}
+
 void page_frag_free(void *addr);
 
 #endif
diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c
index 4666dbec38eb..1e7757a433d0 100644
--- a/mm/page_frag_cache.c
+++ b/mm/page_frag_cache.c
@@ -117,6 +117,27 @@ unsigned int __page_frag_cache_commit_noref(struct page_frag_cache *nc,
 }
 EXPORT_SYMBOL(__page_frag_cache_commit_noref);
 
+void *__page_frag_alloc_refill_probe_align(struct page_frag_cache *nc,
+					   unsigned int fragsz,
+					   struct page_frag *pfrag,
+					   unsigned int align_mask)
+{
+	unsigned long encoded_page = nc->encoded_page;
+	unsigned int size, offset;
+
+	size = page_frag_cache_page_size(encoded_page);
+	offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask);
+	if (unlikely(!encoded_page || offset + fragsz > size))
+		return NULL;
+
+	pfrag->page = page_frag_encoded_page_ptr(encoded_page);
+	pfrag->size = size - offset;
+	pfrag->offset = offset;
+
+	return page_frag_encoded_page_address(encoded_page) + offset;
+}
+EXPORT_SYMBOL(__page_frag_alloc_refill_probe_align);
+
 void *__page_frag_cache_prepare(struct page_frag_cache *nc, unsigned int fragsz,
 				struct page_frag *pfrag, gfp_t gfp_mask,
 				unsigned int align_mask)
-- 
2.33.0