linux-kernel - Re: [PATCH v4 1/3] splice: always fsnotify_access(in), fsnotify

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Message-ID: <CAOQ4uxjqnaB1JJbd3u_oeFsH3V-zYwKftWy=gLhqTQVJvxAgKQ@mail.gmail.com>
Date:   Fri, 30 Jun 2023 14:03:03 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Ahelenia Ziemiańska 
        <nabijaczleweli@...ijaczleweli.xyz>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>,
        Chung-Chiang Cheng <cccheng@...ology.com>, ltp@...ts.linux.it
Subject: Re: [PATCH v4 1/3] splice: always fsnotify_access(in),
 fsnotify_modify(out) on success

On Wed, Jun 28, 2023 at 11:18 PM Ahelenia Ziemiańska
<nabijaczleweli@...ijaczleweli.xyz> wrote:
>
> On Wed, Jun 28, 2023 at 09:38:03PM +0300, Amir Goldstein wrote:
> > On Wed, Jun 28, 2023 at 8:09 PM Ahelenia Ziemiańska
> > <nabijaczleweli@...ijaczleweli.xyz> wrote:
> > > On Wed, Jun 28, 2023 at 09:33:43AM +0300, Amir Goldstein wrote:
> > > > I think we need to add a rule to fanotify_events_supported() to ban
> > > > sb/mount marks on SB_KERNMOUNT and backport this
> > > > fix to LTS kernels (I will look into it) and then we can fine tune
> > > > the s_fsnotify_connectors optimization in fsnotify_parent() for
> > > > the SB_KERNMOUNT special case.
> > > > This may be able to save your patch for the faith of NACKed
> > > > for performance regression.
> > > This goes over my head, but if Jan says it makes sense
> > > then it must do.
> > Here you go:
> > https://github.com/amir73il/linux/commits/fsnotify_pipe
> >
> > I ended up using SB_NOUSER which is narrower than
> > SB_KERNMOUNT.
> >
> > Care to test?
> > 1) Functionally - that I did not break your tests.
> ) | gzip -d > inotify13; chmod +x inotify13; exec ./inotify13
> tst_test.c:1560: TINFO: Timeout per run is 0h 00m 30s
> inotify13.c:260: TINFO: file_to_pipe
> inotify13.c:269: TPASS: ок
> inotify13.c:260: TINFO: file_to_pipe
> inotify13.c:269: TPASS: ок
> inotify13.c:260: TINFO: splice_pipe_to_file
> inotify13.c:269: TPASS: ок
> inotify13.c:260: TINFO: pipe_to_pipe
> inotify13.c:269: TPASS: ок
> inotify13.c:260: TINFO: pipe_to_pipe
> inotify13.c:269: TPASS: ок
> inotify13.c:260: TINFO: vmsplice_pipe_to_mem
> inotify13.c:269: TPASS: ок
> inotify13.c:260: TINFO: vmsplice_mem_to_pipe
> inotify13.c:269: TPASS: ок
>
> Summary:
> passed   7
> failed   0
> broken   0
> skipped  0
> warnings 0
>
> The discrete tests from before also work as expected,
> both to a fifo and an anon pipe.
>
> > 2) Optimization - that when one anon pipe has an inotify watch
> > write to another anon pipe stops at fsnotify_inode_has_watchers()
> > and does not get to fsnotify().
> Yes, I can confirm this as well: fsnotify_parent() only continues to
> fsnotify() for the watched pipe; writes to other pipes early-exit.
>
> To validate the counterfactual, I reverted "fsnotify: optimize the case
> of anonymous pipe with no watches" and fsnotify() was being called
> for each anon pipe write, so long as any anon pipe watches were registered.

Thank you for testing!

As Jan suggested, when you post v5, with my Reviewed-by and Jan's
Acked-by, please ask Christian to review and consider taking these
patches through the vfs tree for the 6.6 release.

Please include a link to your LTP test in the cover letter and a link to
my performance optimization patches.

Unless the kernel test bots detect a performance regression due to
your patches, I am not sure whether or not or when we will apply the
optimization patches.

Thanks,
Amir.