archives/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-03-08 05:24:39 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

fs/file: optimize close_range() complexity from O(N) to O(Sparse)

Browse source 
In close_range(), the kernel traditionally performs a linear scan over the
[fd, max_fd] range, resulting in O(N) complexity where N is the range size.
For processes with sparse FD tables, this is inefficient as it checks many
unallocated slots.

This patch optimizes __range_close() by using find_next_bit() on the
open_fds bitmap to skip holes. This shifts the algorithmic complexity from
O(Range Size) to O(Active FDs), providing a significant performance boost
for large-range close operations on sparse file descriptor tables.

Signed-off-by: Qiliang Yuan <realwujing@gmail.com>
Signed-off-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
Link: https://patch.msgid.link/20260123081221.659125-1-realwujing@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Qiliang Yuan 2026-01-23 03:12:21 -05:00 • committed by Christian Brauner
parent 6cbfdf8947
commit fc94368bce
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
1 changed files with 8 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

10
fs/file.c
View file

@ -777,23 +777,29 @@ static inline void __range_close(struct files_struct *files, unsigned int fd,
unsigned int max_fd)
{
struct file *file;
struct fdtable *fdt;
unsigned n;
spin_lock(&files->file_lock);
n = last_fd(files_fdtable(files));
fdt = files_fdtable(files);
n = last_fd(fdt);
max_fd = min(max_fd, n);
for (; fd <= max_fd; fd++) {
for (fd = find_next_bit(fdt->open_fds, max_fd + 1, fd);
fd <= max_fd;
fd = find_next_bit(fdt->open_fds, max_fd + 1, fd + 1)) {
file = file_close_fd_locked(files, fd);
if (file) {
spin_unlock(&files->file_lock);
filp_close(file, files);
cond_resched();
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
} else if (need_resched()) {
spin_unlock(&files->file_lock);
cond_resched();
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
}
}
spin_unlock(&files->file_lock);