[PATCH v5 2/3] MTD: Retry Large Buffer Allocations
Grant Erickson
marathon96 at gmail.com
Fri Apr 8 11:51:33 EDT 2011
Replace direct call to kmalloc for a potentially large, contiguous
buffer allocation with one to mtd_kmalloc_up_to which helps ensure the
operation can succeed under low-memory, highly- fragmented situations
albeit somewhat more slowly.
Signed-off-by: Grant Erickson <marathon96 at gmail.com>
Tested-by: Ben Gardiner <bengardiner at nanometrics.ca>
---
drivers/mtd/mtdchar.c | 50 ++++++++++++++++++++++--------------------------
1 files changed, 23 insertions(+), 27 deletions(-)
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 145b3d0d..9301464 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -166,10 +166,23 @@ static int mtd_close(struct inode *inode, struct file *file)
return 0;
} /* mtd_close */
-/* FIXME: This _really_ needs to die. In 2.5, we should lock the
- userspace buffer down and use it directly with readv/writev.
-*/
-#define MAX_KMALLOC_SIZE 0x20000
+/* Back in April 2005, Linus wrote:
+ *
+ * FIXME: This _really_ needs to die. In 2.5, we should lock the
+ * userspace buffer down and use it directly with readv/writev.
+ *
+ * The implementation below, using mtd_kmalloc_up_to, mitigates
+ * allocation failures when the system is under low-memory situations
+ * or if memory is highly fragmented at the cost of reducing the
+ * performance of the requested transfer due to a smaller buffer size.
+ *
+ * A more complex but more memory-efficient implementation based on
+ * get_user_pages and iovecs to cover extents of those pages is a
+ * longer-term goal, as intimated by Linus above. However, for the
+ * write case, this requires yet more complex head and tail transfer
+ * handling when those head and tail offsets and sizes are such that
+ * alignment requirements are not met in the NAND subdriver.
+ */
static ssize_t mtd_read(struct file *file, char __user *buf, size_t count,loff_t *ppos)
{
@@ -179,6 +192,7 @@ static ssize_t mtd_read(struct file *file, char __user *buf, size_t count,loff_t
size_t total_retlen=0;
int ret=0;
int len;
+ size_t size = count;
char *kbuf;
DEBUG(MTD_DEBUG_LEVEL0,"MTD_read\n");
@@ -189,23 +203,12 @@ static ssize_t mtd_read(struct file *file, char __user *buf, size_t count,loff_t
if (!count)
return 0;
- /* FIXME: Use kiovec in 2.5 to lock down the user's buffers
- and pass them directly to the MTD functions */
-
- if (count > MAX_KMALLOC_SIZE)
- kbuf=kmalloc(MAX_KMALLOC_SIZE, GFP_KERNEL);
- else
- kbuf=kmalloc(count, GFP_KERNEL);
-
+ kbuf = mtd_kmalloc_up_to(&size);
if (!kbuf)
return -ENOMEM;
while (count) {
-
- if (count > MAX_KMALLOC_SIZE)
- len = MAX_KMALLOC_SIZE;
- else
- len = count;
+ len = min_t(size_t, count, size);
switch (mfi->mode) {
case MTD_MODE_OTP_FACTORY:
@@ -268,6 +271,7 @@ static ssize_t mtd_write(struct file *file, const char __user *buf, size_t count
{
struct mtd_file_info *mfi = file->private_data;
struct mtd_info *mtd = mfi->mtd;
+ size_t size = count;
char *kbuf;
size_t retlen;
size_t total_retlen=0;
@@ -285,21 +289,12 @@ static ssize_t mtd_write(struct file *file, const char __user *buf, size_t count
if (!count)
return 0;
- if (count > MAX_KMALLOC_SIZE)
- kbuf=kmalloc(MAX_KMALLOC_SIZE, GFP_KERNEL);
- else
- kbuf=kmalloc(count, GFP_KERNEL);
-
+ kbuf = mtd_kmalloc_up_to(&size);
if (!kbuf)
return -ENOMEM;
while (count) {
-
- if (count > MAX_KMALLOC_SIZE)
- len = MAX_KMALLOC_SIZE;
- else
- len = count;
+ len = min_t(size_t, count, size);
if (copy_from_user(kbuf, buf, len)) {
kfree(kbuf);
--
1.7.4.2
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