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Subject[patch 4/4 -mm] flex_array: add flex_array_shrink function
This patch adds a new function to the flex_array API:

int flex_array_shrink(struct flex_array *fa)

This function will free all unused second-level pages. Since elements
are now poisoned if they are not allocated with __GFP_ZERO, it's
possible to identify parts that consist solely of unused elements.

flex_array_shrink() returns the number of pages freed.

Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
include/linux/flex_array.h | 1 +
lib/flex_array.c | 40 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 0 deletions(-)
diff --git a/include/linux/flex_array.h b/include/linux/flex_array.h
--- a/include/linux/flex_array.h
+++ b/include/linux/flex_array.h
@@ -46,5 +46,6 @@ int flex_array_put(struct flex_array *fa, unsigned int element_nr, void *src,
gfp_t flags);
int flex_array_clear(struct flex_array *fa, unsigned int element_nr);
void *flex_array_get(struct flex_array *fa, unsigned int element_nr);
+int flex_array_shrink(struct flex_array *fa);

#endif /* _FLEX_ARRAY_H */
diff --git a/lib/flex_array.c b/lib/flex_array.c
--- a/lib/flex_array.c
+++ b/lib/flex_array.c
@@ -291,3 +291,43 @@ void *flex_array_get(struct flex_array *fa, unsigned int element_nr)
}
return &part->elements[index_inside_part(fa, element_nr)];
}
+
+static int part_is_free(struct flex_array_part *part)
+{
+ int i;
+
+ for (i = 0; i < sizeof(struct flex_array_part); i++)
+ if (part->elements[i] != FLEX_ARRAY_FREE)
+ return 0;
+ return 1;
+}
+
+/**
+ * flex_array_shrink - free unused second-level pages
+ *
+ * Frees all second-level pages that consist solely of unused
+ * elements. Returns the number of pages freed.
+ *
+ * Locking must be provided by the caller.
+ */
+int flex_array_shrink(struct flex_array *fa)
+{
+ struct flex_array_part *part;
+ int max_part = nr_base_part_ptrs();
+ int part_nr;
+ int ret = 0;
+
+ if (elements_fit_in_base(fa))
+ return ret;
+ for (part_nr = 0; part_nr < max_part; part_nr++) {
+ part = fa->parts[part_nr];
+ if (!part)
+ continue;
+ if (part_is_free(part)) {
+ fa->parts[part_nr] = NULL;
+ kfree(part);
+ ret++;
+ }
+ }
+ return ret;
+}

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