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	Sat, 11 May 2024 19:24:03 +0000
Date: Sat, 11 May 2024 20:24:03 +0100
From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: brauner@kernel.org, jack@suse.cz, laoar.shao@gmail.com,
	linux-fsdevel@vger.kernel.org, longman@redhat.com,
	walters@verbum.org, wangkai86@huawei.com, willy@infradead.org
Subject: Re: [PATCH] vfs: move dentry shrinking outside the inode lock in
 'rmdir()'
Message-ID: <20240511192403.GB2118490@ZenIV>
References: <CAHk-=whvo+r-VZH7Myr9fid=zspMo2-0BUJw5S=VTm72iEXXvQ@mail.gmail.com>
 <20240511182625.6717-2-torvalds@linux-foundation.org>
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Sender: Al Viro <viro@ftp.linux.org.uk>

On Sat, May 11, 2024 at 11:26:26AM -0700, Linus Torvalds wrote:
> Yafang Shao reports that he has seen loads that generate billions of
> negative dentries in a directory, which then when the directory is
> removed causes excessive latencies for other users because the dentry
> shrinking is done under the directory inode lock.
> 
> There seems to be no actual reason for holding the inode lock any more
> by the time we get rid of the now uninteresting negative dentries, and
> it's an effect of just code layout (the shared error path).
> 
> Reorganize the code trivially to just have a separate success path,
> which simplifies the code (since 'd_delete_notify()' is only called in
> the success path anyway) and makes it trivial to just move the dentry
> shrinking outside the inode lock.

Wait, I thought he had confirmed that in the setup in question directories
were *not* removed, hadn't he?

I've no objections against that patch, but if the above is accurate it's
not going to help...