Patchwork Retry Large Buffer Allocations

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Submitter Grant Erickson
Date April 5, 2011, 6:34 p.m.
Message ID <1302028464-9519-1-git-send-email-marathon96@gmail.com>
Download mbox | patch
Permalink /patch/89919/
State New
Headers show

Comments

Grant Erickson - April 5, 2011, 6:34 p.m.
When handling user space read or write requests via mtd_{read,write}
or JFFS2 medium scan requests, exponentially back off on the size of
the requested kernel transfer buffer until it succeeds or until the
requested transfer buffer size falls below the page size.

This helps ensure the operation can succeed under low-memory,
highly-fragmented situations albeit somewhat more slowly.

---
 drivers/mtd/mtdchar.c   |   50 +++++++++++++++++++++-------------------------
 drivers/mtd/mtdcore.c   |   31 +++++++++++++++++++++++++++++
 fs/jffs2/scan.c         |   11 +++++----
 include/linux/mtd/mtd.h |    2 +
 4 files changed, 62 insertions(+), 32 deletions(-)

1.7.4.2
Artem Bityutskiy - April 5, 2011, 7:31 p.m.
Just partial review before I go to bed, to keep you busy :-)))

On Tue, 2011-04-05 at 11:34 -0700, Grant Erickson wrote:
> 			kfree(kbuf);
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index da69bc8..d102b96 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -638,6 +638,36 @@ int default_mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
>  	return ret;
>  }
>  
> +/* mtd_alloc_up_to - 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.
> + */

Please, make the comment to be of proper style. See the CodingStyle
file. Or even better - make it proper kerneldoc comment, if you can. I'm
sure you'll find the rules in the "Documentation" directory, but this is
optional. Also, please, put the comment just above the function. 
> +#define MAX_KMALLOC_SIZE 0x20000
> +
> +void *mtd_alloc_up_to(size_t *size)
> +{
> +	gfp_t flags;
> +	size_t try;
> +	void *kbuf;
> +
> +	try = min_t(size_t, *size, MAX_KMALLOC_SIZE);
> +
> +	do {
> +		flags = ((size == PAGE_SIZE) ?

s/size/try/

> +			 GFP_KERNEL :
> +			 (__GFP_NOWARN | __GFP_WAIT |
> +			   __GFP_NORETRY | __GFP_NO_KSWAPD));

Sorry, but this construct is not beautiful and difficult to read. I'd
call it abuse of ?: operators :-) I think it is much more readable to
simply:

1. initialize gfp_t flags to (__GFP_NOWARN .... ) when you initialize it
or just before the loop.
2. Do
	if (try == PAGE_SIZE)
		flags = GFP_KERNEL;

Simple and readable.

And do not forget to check the code with checkpatch.pl before sending
out :-)

Good night!

Patch

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 145b3d0d..fd05a78 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_alloc_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_alloc_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;
@@ -285,20 +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_alloc_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);
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index da69bc8..d102b96 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -638,6 +638,36 @@  int default_mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
 	return ret;
 }
 
+/* mtd_alloc_up_to - 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.
+ */
+
+#define MAX_KMALLOC_SIZE 0x20000
+
+void *mtd_alloc_up_to(size_t *size)
+{
+	gfp_t flags;
+	size_t try;
+	void *kbuf;
+
+	try = min_t(size_t, *size, MAX_KMALLOC_SIZE);
+
+	do {
+		flags = ((size == PAGE_SIZE) ?
+			 GFP_KERNEL :
+			 (__GFP_NOWARN | __GFP_WAIT |
+			   __GFP_NORETRY | __GFP_NO_KSWAPD));
+
+		kbuf = kmalloc(try, flags);
+	} while (!kbuf && ((try >>= 1) >= PAGE_SIZE));
+
+	*size = try;
+
+	return kbuf;
+}
+
 EXPORT_SYMBOL_GPL(add_mtd_device);
 EXPORT_SYMBOL_GPL(del_mtd_device);
 EXPORT_SYMBOL_GPL(get_mtd_device);
@@ -648,6 +678,7 @@  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_alloc_up_to);
 
 #ifdef CONFIG_PROC_FS
 
diff --git a/fs/jffs2/scan.c b/fs/jffs2/scan.c
index b632ddd..42a28b1 100644
--- a/fs/jffs2/scan.c
+++ b/fs/jffs2/scan.c
@@ -117,14 +117,15 @@  int jffs2_scan_medium(struct jffs2_sb_info *c)
 		else
 			buf_size = PAGE_SIZE;
 
-		/* Respect kmalloc limitations */
-		if (buf_size > 128*1024)
-			buf_size = 128*1024;
+		D1(printk(KERN_DEBUG "Trying to allocate readbuf of %d "
+			"bytes\n", buf_size));
 
-		D1(printk(KERN_DEBUG "Allocating readbuf of %d bytes\n", buf_size));
-		flashbuf = kmalloc(buf_size, GFP_KERNEL);
+		flashbuf = mtd_alloc_up_to(&buf_size);
 		if (!flashbuf)
 			return -ENOMEM;
+
+		D1(printk(KERN_DEBUG "Allocated readbuf of %d bytes\n",
+			buf_size));
 	}
 
 	if (jffs2_sum_active()) {
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 9d5306b..44c4c45 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -348,7 +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_alloc_up_to(size_t *size);
+
 #ifdef CONFIG_MTD_PARTITIONS
 void mtd_erase_callback(struct erase_info *instr);
 #else
--