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From: Jan Kara <jack@suse.cz>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Jan Kara <jack@suse.cz>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH 01/20] fsnotify: Rearrange fast path to minimise overhead when there is no watcher
Date: Mon, 6 Jul 2020 13:05:26 +0200	[thread overview]
Message-ID: <20200706110526.GA3913@quack2.suse.cz> (raw)
In-Reply-To: <CAOQ4uxgJkmSgt6nSO3C4y2Mc=T92ky5K5eis0f1Ofr-wDq7Wrw@mail.gmail.com>

On Sat 04-07-20 12:30:10, Amir Goldstein wrote:
> On Fri, Jul 3, 2020 at 5:03 PM Jan Kara <jack@suse.cz> wrote:
> > >  /* Notify this dentry's parent about a child's events. */
> > > -int fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data,
> > > +int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data,
> > >                   int data_type)
> > >  {
> > >       struct dentry *parent;
> >
> > Hum, should we actually remove the DCACHE_FSNOTIFY_PARENT_WATCHED check
> > from here when it's moved to fsnotify_parent() inline helper?
> 
> No point.
> It is making a comeback on:
>  fsnotify: send event with parent/name info to sb/mount/non-dir marks

Right, I've noticed that later as well.

> > > @@ -337,13 +331,22 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
> > >       if (!to_tell->i_fsnotify_marks && !sb->s_fsnotify_marks &&
> > >           (!mnt || !mnt->mnt_fsnotify_marks))
> > >               return 0;
> > > +
> > > +     /* An event "on child" is not intended for a mount/sb mark */
> > > +     marks_mask = to_tell->i_fsnotify_mask;
> > > +     if (!(mask & FS_EVENT_ON_CHILD)) {
> > > +             marks_mask |= sb->s_fsnotify_mask;
> > > +             if (mnt)
> > > +                     marks_mask |= mnt->mnt_fsnotify_mask;
> > > +     }
> > > +
> > >       /*
> > >        * if this is a modify event we may need to clear the ignored masks
> > >        * otherwise return if neither the inode nor the vfsmount/sb care about
> > >        * this type of event.
> > >        */
> > > -     if (!(mask & FS_MODIFY) &&
> > > -         !(test_mask & (to_tell->i_fsnotify_mask | mnt_or_sb_mask)))
> > > +     test_mask = (mask & ALL_FSNOTIFY_EVENTS);
> > > +     if (!(mask & FS_MODIFY) && !(test_mask & marks_mask))
> > >               return 0;
> >
> > Otherwise the patch looks good. One observation though: The (mask &
> > FS_MODIFY) check means that all vfs_write() calls end up going through the
> > "slower" path iterating all mark types and checking whether there are marks
> > anyway. That could be relatively simply optimized using a hidden mask flag
> > like FS_ALWAYS_RECEIVE_MODIFY which would be set when there's some mark
> > needing special handling of FS_MODIFY... Not sure if we care enough at this
> > point...
> 
> Yeh that sounds low hanging.
> Actually, I Don't think we need to define a flag for that.
> __fsnotify_recalc_mask() can add FS_MODIFY to the object's mask if needed.

Yes, that would be even more elegant.

> I will take a look at that as part of FS_PRE_MODIFY work.
> But in general, we should fight the urge to optimize theoretic
> performance issues...

Agreed. I just suspect this may bring measurable benefit for hackbench pipe
or tiny tmpfs writes after seeing Mel's results. But as I wrote this is a
separate idea and without some numbers confirming my suspicion I don't
think the complication is worth it so I don't want you to burn time on this
unless you're really interested :).

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply	other threads:[~2020-07-06 11:05 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12  9:33 [PATCH 00/20] Prep work for fanotify named events Amir Goldstein
2020-06-12  9:33 ` [PATCH 01/20] fsnotify: Rearrange fast path to minimise overhead when there is no watcher Amir Goldstein
2020-07-03 14:03   ` Jan Kara
2020-07-04  9:30     ` Amir Goldstein
2020-07-06 11:05       ` Jan Kara [this message]
2020-07-09 17:56         ` fsnotify: minimise overhead when there are no marks with ignore mask Amir Goldstein
2020-07-26 15:20           ` fsnotify: minimise overhead when there are no marks related to sb Amir Goldstein
2020-07-27  7:44             ` Jan Kara
2020-07-27 10:02               ` Amir Goldstein
2020-06-12  9:33 ` [PATCH 02/20] fsnotify: fold fsnotify() call into fsnotify_parent() Amir Goldstein
2020-06-12  9:33 ` [PATCH 03/20] fsnotify: return non const from fsnotify_data_inode() Amir Goldstein
2020-06-12  9:33 ` [PATCH 04/20] nfsd: use fsnotify_data_inode() to get the unlinked inode Amir Goldstein
2020-06-12 10:25   ` Amir Goldstein
2020-06-12  9:33 ` [PATCH 05/20] kernfs: do not call fsnotify() with name without a parent Amir Goldstein
2020-06-29 13:27   ` Tejun Heo
2020-06-29 16:11   ` Greg Kroah-Hartman
2020-06-12  9:33 ` [PATCH 06/20] inotify: do not use objectid when comparing events Amir Goldstein
2020-06-12  9:33 ` [PATCH 07/20] fanotify: create overflow event type Amir Goldstein
2020-06-12  9:33 ` [PATCH 08/20] fanotify: break up fanotify_alloc_event() Amir Goldstein
2020-06-12  9:33 ` [PATCH 09/20] fsnotify: pass dir argument to handle_event() callback Amir Goldstein
2020-07-03 14:49   ` Jan Kara
2020-06-12  9:33 ` [PATCH 10/20] fanotify: generalize the handling of extra event flags Amir Goldstein
2020-06-12  9:33 ` [PATCH 11/20] fanotify: generalize merge logic of events on dir Amir Goldstein
2020-06-12  9:33 ` [PATCH 12/20] fanotify: distinguish between fid encode error and null fid Amir Goldstein
2020-06-12  9:33 ` [PATCH 13/20] fanotify: generalize test for FAN_REPORT_FID Amir Goldstein
2020-06-12  9:33 ` [PATCH 14/20] fanotify: mask out special event flags from ignored mask Amir Goldstein
2020-06-12  9:33 ` [PATCH 15/20] fanotify: prepare for implicit event flags in mark mask Amir Goldstein
2020-06-12  9:33 ` [PATCH 16/20] fanotify: use FAN_EVENT_ON_CHILD as implicit flag on sb/mount/non-dir marks Amir Goldstein
2020-06-12  9:33 ` [PATCH 17/20] fanotify: remove event FAN_DIR_MODIFY Amir Goldstein
2020-06-12  9:33 ` [PATCH 18/20] fsnotify: add object type "child" to object type iterator Amir Goldstein
2020-06-12  9:33 ` [PATCH 19/20] fanotify: move event name into fanotify_fh Amir Goldstein
2020-07-03 16:02   ` Jan Kara
2020-07-06  8:21     ` Amir Goldstein
2020-07-06 15:24       ` Jan Kara
2020-06-12  9:33 ` [PATCH 20/20] fanotify: no external fh buffer in fanotify_name_event Amir Goldstein

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