On Thu 11-01-24 17:22:33, Amir Goldstein wrote:
> Commit e43de7f0862b ("fsnotify: optimize the case of no marks of any type")
> optimized the case where there are no fsnotify watchers on any of the
> filesystem's objects.
>
> It is quite common for a system to have a single local filesystem and
> it is quite common for the system to have some inotify watches on some
> config files or directories, so the optimization of no marks at all is
> often not in effect.
>
> Content event (i.e. access,modify) watchers on sb/mount more rare, so
> optimizing the case of no sb/mount marks with content events can improve
> performance for more systems, especially for performance sensitive io
> workloads.
>
> Set a per-sb flag SB_I_CONTENT_WATCHED if sb/mount marks with content
> events in their mask exist and use that flag to optimize out the call to
> __fsnotify_parent() and fsnotify() in fsnotify access/modify hooks.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
...
> -static inline int fsnotify_file(struct file *file, __u32 mask)
> +static inline int fsnotify_path(const struct path *path, __u32 mask)
> {
> - const struct path *path;
> + struct dentry *dentry = path->dentry;
>
> - if (file->f_mode & FMODE_NONOTIFY)
> + if (!fsnotify_sb_has_watchers(dentry->d_sb))
> return 0;
>
> - path = &file->f_path;
> + /* Optimize the likely case of sb/mount/parent not watching content */
> + if (mask & FSNOTIFY_CONTENT_EVENTS &&
> + likely(!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED)) &&
> + likely(!(dentry->d_sb->s_iflags & SB_I_CONTENT_WATCHED))) {
> + /*
> + * XXX: if SB_I_CONTENT_WATCHED is not set, checking for content
> + * events in s_fsnotify_mask is redundant, but it will be needed
> + * if we use the flag FS_MNT_CONTENT_WATCHED to indicate the
> + * existence of only mount content event watchers.
> + */
> + __u32 marks_mask = d_inode(dentry)->i_fsnotify_mask |
> + dentry->d_sb->s_fsnotify_mask;
> +
> + if (!(mask & marks_mask))
> + return 0;
> + }
So I'm probably missing something but how is all this patch different from:
if (likely(!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))) {
__u32 marks_mask = d_inode(dentry)->i_fsnotify_mask |
path->mnt->mnt_fsnotify_mask |
dentry->d_sb->s_fsnotify_mask;
if (!(mask & marks_mask))
return 0;
}
I mean (mask & FSNOTIFY_CONTENT_EVENTS) is true for the frequent events
(read & write) we care about. In Jens' case
!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED) &&
!(dentry->d_sb->s_iflags & SB_I_CONTENT_WATCHED)
is true as otherwise we'd go right to fsnotify_parent() and so Jens
wouldn't see the performance benefit. But then with your patch you fetch
i_fsnotify_mask and s_fsnotify_mask anyway for the test so the only
difference to what I suggest above is the path->mnt->mnt_fsnotify_mask
fetch but that is equivalent to sb->s_iflags (or wherever we store that
bit) fetch?
So that would confirm that the parent handling costs in fsnotify_parent()
is what's really making the difference and just avoiding that by checking
masks early should be enough?
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
