2 files changed, 51 insertions, 0 deletions

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index da69bc8a5a7d..a50348b60d79 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -638,6 +638,54 @@ int default_mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
         return ret;
 }
 
+/**
+ * mtd_kmalloc_up_to - allocate a contiguous buffer up to the specified size
+ * @size: A pointer to the ideal or maximum size of the allocation. Points
+ *        to the actual allocation size on success.
+ *
+ * This routine attempts to allocate a contiguous kernel buffer up to
+ * the specified size, backing off the size of the request exponentially
+ * until the request succeeds or until the allocation size falls below
+ * the system page size. This attempts to make sure it does not adversely
+ * impact system performance, so when allocating more than one page, we
+ * ask the memory allocator to avoid re-trying, swapping, writing back
+ * or performing I/O.
+ *
+ * Note, this function also makes sure that the allocated buffer is aligned to
+ * the MTD device's min. I/O unit, i.e. the "mtd->writesize" value.
+ *
+ * This is called, for example by mtd_{read,write} and jffs2_scan_medium,
+ * to handle smaller (i.e. degraded) buffer allocations under low- or
+ * fragmented-memory situations where such reduced allocations, from a
+ * requested ideal, are allowed.
+ *
+ * Returns a pointer to the allocated buffer on success; otherwise, NULL.
+ */
+void *mtd_kmalloc_up_to(const struct mtd_info *mtd, size_t *size)
+{
+        gfp_t flags = __GFP_NOWARN | __GFP_WAIT |
+                       __GFP_NORETRY | __GFP_NO_KSWAPD;
+        size_t min_alloc = max_t(size_t, mtd->writesize, PAGE_SIZE);
+        void *kbuf;
+
+        *size = min_t(size_t, *size, KMALLOC_MAX_SIZE);
+
+        while (*size > min_alloc) {
+                kbuf = kmalloc(*size, flags);
+                if (kbuf)
+                        return kbuf;
+
+                *size >>= 1;
+                *size = ALIGN(*size, mtd->writesize);
+        }
+
+        /*
+         * For the last resort allocation allow 'kmalloc()' to do all sorts of
+         * things (write-back, dropping caches, etc) by using GFP_KERNEL.
+         */
+        return kmalloc(*size, GFP_KERNEL);
+}
+
 EXPORT_SYMBOL_GPL(add_mtd_device);
 EXPORT_SYMBOL_GPL(del_mtd_device);
 EXPORT_SYMBOL_GPL(get_mtd_device);
@@ -648,6 +696,7 @@ EXPORT_SYMBOL_GPL(__put_mtd_device);
 EXPORT_SYMBOL_GPL(register_mtd_user);
 EXPORT_SYMBOL_GPL(unregister_mtd_user);
 EXPORT_SYMBOL_GPL(default_mtd_writev);
+EXPORT_SYMBOL_GPL(mtd_kmalloc_up_to);
 
 #ifdef CONFIG_PROC_FS
 
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 9d5306bad117..06b489a7605b 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -348,6 +348,8 @@ int default_mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
 int default_mtd_readv(struct mtd_info *mtd, struct kvec *vecs,
                       unsigned long count, loff_t from, size_t *retlen);
 
+void *mtd_kmalloc_up_to(const struct mtd_info *mtd, size_t *size);
+
 #ifdef CONFIG_MTD_PARTITIONS
 void mtd_erase_callback(struct erase_info *instr);
 #else