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Commit aa82126d authored by Sultan Alsawaf's avatar Sultan Alsawaf Committed by Gagan Malvi
Browse files

kernfs: Avoid dynamic memory allocation for small write buffers 



Most write buffers are rather small and can fit on the stack,
eliminating the need to allocate them dynamically. Reserve a 4 KiB
stack buffer for this purpose to avoid the overhead of dynamic
memory allocation.

Signed-off-by: default avatarSultan Alsawaf <sultan@kerneltoast.com>
parent 67ebf95f

fs/kernfs/file.c

+12 −6
Original line number Original line Diff line number Diff line
@@ -273,6 +273,7 @@ static ssize_t kernfs_fop_read(struct file *file, char __user *user_buf, 
static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,

static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,

				size_t count, loff_t *ppos)

				size_t count, loff_t *ppos)

{

{

	char buf_onstack[SZ_4K + 1] __aligned(sizeof(long));

	struct kernfs_open_file *of = kernfs_of(file);

	struct kernfs_open_file *of = kernfs_of(file);

	const struct kernfs_ops *ops;

	const struct kernfs_ops *ops;

	ssize_t len;

	ssize_t len;
@@ -287,12 +288,17 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf, 
	}

	}





	buf = of->prealloc_buf;

	buf = of->prealloc_buf;

	if (buf)

	if (buf) {

		mutex_lock(&of->prealloc_mutex);

		mutex_lock(&of->prealloc_mutex);

	else

	} else {

		if (len < ARRAY_SIZE(buf_onstack)) {

			buf = buf_onstack;

		} else {

			buf = kmalloc(len + 1, GFP_KERNEL);

			buf = kmalloc(len + 1, GFP_KERNEL);

			if (!buf)

			if (!buf)

				return -ENOMEM;

				return -ENOMEM;

		}

	}





	if (copy_from_user(buf, user_buf, len)) {

	if (copy_from_user(buf, user_buf, len)) {

		len = -EFAULT;

		len = -EFAULT;
@@ -326,7 +332,7 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf, 
out_free:

out_free:

	if (buf == of->prealloc_buf)

	if (buf == of->prealloc_buf)

		mutex_unlock(&of->prealloc_mutex);

		mutex_unlock(&of->prealloc_mutex);

	else

	else if (buf != buf_onstack)

		kfree(buf);

		kfree(buf);

	return len;

	return len;

}

}