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-rw-r--r--include/linux/scatterlist.h25
1 files changed, 25 insertions, 0 deletions
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 556ec1ea2574..cb3c8fe6acd7 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -286,6 +286,31 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
#define SG_MAX_SINGLE_ALLOC (PAGE_SIZE / sizeof(struct scatterlist))
/*
+ * The maximum number of SG segments that we will put inside a
+ * scatterlist (unless chaining is used). Should ideally fit inside a
+ * single page, to avoid a higher order allocation. We could define this
+ * to SG_MAX_SINGLE_ALLOC to pack correctly at the highest order. The
+ * minimum value is 32
+ */
+#define SG_CHUNK_SIZE 128
+
+/*
+ * Like SG_CHUNK_SIZE, but for archs that have sg chaining. This limit
+ * is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
+ */
+#ifdef CONFIG_ARCH_HAS_SG_CHAIN
+#define SG_MAX_SEGMENTS 2048
+#else
+#define SG_MAX_SEGMENTS SG_CHUNK_SIZE
+#endif
+
+#ifdef CONFIG_SG_POOL
+void sg_free_table_chained(struct sg_table *table, bool first_chunk);
+int sg_alloc_table_chained(struct sg_table *table, int nents,
+ struct scatterlist *first_chunk);
+#endif
+
+/*
* sg page iterator
*
* Iterates over sg entries page-by-page. On each successful iteration,