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kernfs: Avoid dynamic memory allocation for small write buffers

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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: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: azrim <mirzaspc@gmail.com>
This commit is contained in:
Sultan Alsawaf 2021-02-04 21:42:50 -08:00 committed by azrim
parent 875f389399
commit 132d8d5380
No known key found for this signature in database
GPG Key ID: 497F8FB059B45D1C
1 changed files with 12 additions and 6 deletions
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18
fs/kernfs/file.c
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@ -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,
size_t count, loff_t *ppos)
{
char buf_onstack[SZ_4K + 1] __aligned(sizeof(long));
struct kernfs_open_file *of = kernfs_of(file);
const struct kernfs_ops *ops;
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;
if (buf)
if (buf) {
mutex_lock(&of->prealloc_mutex);
else
buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
} else {
if (len < ARRAY_SIZE(buf_onstack)) {
buf = buf_onstack;
} else {
buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
}
}
if (copy_from_user(buf, user_buf, len)) {
len = -EFAULT;
@ -326,7 +332,7 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
out_free:
if (buf == of->prealloc_buf)
mutex_unlock(&of->prealloc_mutex);
else
else if (buf != buf_onstack)
kfree(buf);
return len;
}