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>

diff --git a/fs/dcache.c b/fs/dcache.c
index 29d58212aaf02bc039a84ffc7ad998e176a3025c..91e551b5af59402eb9d2d5fa1261d9b5a299824a 100644 (file)
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -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;
 }