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vfs: use __getname/__putname for getcwd() system call 

It's a pathname.  It should use the pathname allocators and
deallocators, and PATH_MAX instead of PAGE_SIZE.  Never mind that the
two are commonly the same.

With this, the allocations scale up nicely too, and I can do getcwd()
system calls at a rate of about 300M/s, with no lock contention
anywhere.

Of course, nobody sane does that, especially since getcwd() is
traditionally a very slow operation in Unix.  But this was also the
simplest way to benchmark the prepend_path() improvements by Waiman, and
once I saw the profiles I couldn't leave it well enough alone.

But apart from being an performance improvement (from using per-cpu slab
allocators instead of the raw page allocator), it's actually a valid and
real cleanup.

Signed-off-by: Linus "OCD" Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2013-09-12 12:40:15 -07:00
parent ff812d7242
commit 3272c544da
1 changed files with 5 additions and 5 deletions
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10
fs/dcache.c
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@ -3049,7 +3049,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
{
int error;
struct path pwd, root;
char *page = (char *) __get_free_page(GFP_USER);
char *page = __getname();
if (!page)
return -ENOMEM;
@ -3061,8 +3061,8 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
br_read_lock(&vfsmount_lock);
if (!d_unlinked(pwd.dentry)) {
unsigned long len;
char *cwd = page + PAGE_SIZE;
int buflen = PAGE_SIZE;
char *cwd = page + PATH_MAX;
int buflen = PATH_MAX;
prepend(&cwd, &buflen, "\0", 1);
error = prepend_path(&pwd, &root, &cwd, &buflen);
@ -3080,7 +3080,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
}
error = -ERANGE;
len = PAGE_SIZE + page - cwd;
len = PATH_MAX + page - cwd;
if (len <= size) {
error = len;
if (copy_to_user(buf, cwd, len))
@ -3092,7 +3092,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned long, size)
}
out:
free_page((unsigned long) page);
__putname(page);
return error;
}