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Date:   Fri, 12 Jun 2020 12:52:28 +0300
From:   Amir Goldstein <>
To:     Mel Gorman <>
Cc:     Jan Kara <>, Alexander Viro <>,
        linux-fsdevel <>,
        linux-kernel <>
Subject: Re: [PATCH] fs: Do not check if there is a fsnotify watcher on pseudo inodes

On Fri, Jun 12, 2020 at 12:26 PM Mel Gorman <> wrote:
> The kernel uses internal mounts for a number of purposes including pipes.
> On every vfs_write regardless of filesystem, fsnotify_modify() is called
> to notify of any changes which incurs a small amount of overhead in fsnotify
> even when there are no watchers.
> A patch is pending that reduces, but does not eliminte, the overhead
> of fsnotify but for the internal mounts, even the small overhead is
> unnecessary. The user API is based on the pathname and a dirfd and proc
> is the only visible path for inodes on an internal mount. Proc does not
> have the same pathname as the internal entry so even if fatrace is used
> on /proc, no events trigger for the /proc/X/fd/ files.

This looks like a good direction and I was going to suggest that as well.
However, I am confused by the use of terminology "internal mount".
The patch does not do anything dealing with "internal mount".
If alloc_file_pseudo() is only called for filesystems mounted as
internal mounts,
please include this analysis in commit message.
In any case, not every file of internal mount is allocated with
right? So maybe it would be better to list all users of alloc_file_pseudo()
and say that they all should be opted out of fsnotify, without mentioning
"internal mount"?


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