[PATCH 10/11] lib/scatterlist: Add sg_trim_table

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 include/linux/scatterlist.h |  2 ++
 lib/scatterlist.c           | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 983a8391d469..46edc9967c74 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -276,6 +276,8 @@ int sg_alloc_table_from_pages(struct sg_table *sgt, struct page **pages,
 			      unsigned int n_pages, unsigned int offset,
 			      unsigned long size, gfp_t gfp_mask);
 
+void sg_trim_table(struct sg_table *st, gfp_t gfp);
+
 #ifdef CONFIG_SGL_ALLOC
 struct scatterlist *
 sgl_alloc_order_min_max(unsigned long length,
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 9595c8feca1e..e57331224622 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -549,6 +549,32 @@ __sg_trim_scatterlist(struct scatterlist *sg,
 	return new;
 }
 
+/**
+ * sg_trim_table - Reallocate the table for minimum scatterlist size
+ *
+ * @st: 	Existing table.
+ * @gfp: 	Allocation flags to use when re-allocating.
+ *
+ * This function reallocates the scatterlist table if the orig_nents is larger
+ * than nents.
+ *
+ * This is useful for avoiding memory waste in cases when lists are built
+ * dynamically, the minimum number of entries is not known before hand, and the
+ * two pass approach is not feasible.
+ */
+void sg_trim_table(struct sg_table *st, gfp_t gfp)
+{
+	struct scatterlist *sg;
+
+	sg = __sg_trim_scatterlist(st->sgl, st->nents, st->orig_nents, gfp);
+
+	if (sg && sg != st->sgl) {
+		st->sgl = sg;
+		st->orig_nents = st->nents;
+	}
+}
+EXPORT_SYMBOL(sg_trim_table);
+
 struct scatterlist *
 sgl_alloc_order_min_max(unsigned long length,
 			unsigned int min_order, unsigned int max_order,
-- 
2.14.1