diff options
| author | Mateusz Guzik <mjguzik@gmail.com> | 2024-06-24 10:54:02 +0200 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2024-06-25 11:15:48 +0200 |
| commit | 8e3447822d7d8c0f562c6851a7a31e24d1ede55e (patch) | |
| tree | e16c35e65568d16c083380d92bfe161127956ae0 /mm | |
| parent | 153216cf7bd50842ffc3d500ea96adeb65db63ef (diff) | |
vfs: remove redundant smp_mb for thp handling in do_dentry_open
opening for write performs:
if (f->f_mode & FMODE_WRITE) {
[snip]
smp_mb();
if (filemap_nr_thps(inode->i_mapping)) {
[snip]
}
}
filemap_nr_thps on kernels built without CONFIG_READ_ONLY_THP_FOR
expands to 0, allowing the compiler to eliminate the entire thing, with
exception of the fence (and the branch leading there).
So happens required synchronisation between i_writecount and nr_thps
changes is already provided by the full fence coming from
get_write_access -> atomic_inc_unless_negative, thus the smp_mb instance
above can be removed regardless of CONFIG_READ_ONLY_THP_FOR.
While I updated commentary in places claiming to match the now-removed
fence, I did not try to patch them to act on the compile option.
I did not bother benchmarking it, not issuing a spurious full fence in
the fast path does not warrant justification from perf standpoint.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240624085402.493630-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/khugepaged.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 774a97e6e2da..aab471791bd9 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2000,9 +2000,9 @@ out_unlock: if (!is_shmem) { filemap_nr_thps_inc(mapping); /* - * Paired with smp_mb() in do_dentry_open() to ensure - * i_writecount is up to date and the update to nr_thps is - * visible. Ensures the page cache will be truncated if the + * Paired with the fence in do_dentry_open() -> get_write_access() + * to ensure i_writecount is up to date and the update to nr_thps + * is visible. Ensures the page cache will be truncated if the * file is opened writable. */ smp_mb(); @@ -2190,8 +2190,8 @@ rollback: if (!is_shmem && result == SCAN_COPY_MC) { filemap_nr_thps_dec(mapping); /* - * Paired with smp_mb() in do_dentry_open() to - * ensure the update to nr_thps is visible. + * Paired with the fence in do_dentry_open() -> get_write_access() + * to ensure the update to nr_thps is visible. */ smp_mb(); } |