linux-kernel - Re: [patch 3/7] fs, notify: Add file handle entry into inotify_inode

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Message-Id: <20121112234001.009b2ae3.akpm@linux-foundation.org>
Date:	Mon, 12 Nov 2012 23:40:01 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>,
	aneesh.kumar@...ux.vnet.ibm.com, bfields@...ldses.org
Subject: Re: [patch 3/7] fs, notify: Add file handle entry into
 inotify_inode_mark

On Tue, 13 Nov 2012 11:20:57 +0400 Cyrill Gorcunov <gorcunov@...nvz.org> wrote:

> > >  struct inotify_inode_mark {
> > >  	struct fsnotify_mark fsn_mark;
> > >  	int wd;
> > > +#ifdef INOTIFY_USE_FHANDLE
> > > +	__u8 fhandle[sizeof(struct file_handle) + MAX_HANDLE_SZ];
> > > +#endif
> > >  };
> > 
> > Whoa.  This adds 128+8 bytes to the inotify_inode_mark.  That's a lot of
> > bloat, and there can be a lot of inotify_inode_mark's in the system?
> 
> Yes, that's why it's not turned on by default, only if is c/r turned on.
> iirc I've been said that usually only about 40 bytes is used (in the tests
> I met only 8 bytes). Letme re-check all things.

The question is, how many `struct inotify_inode_mark's are instantiated
system-wide?  Could be millions?

Dumb question: do we really need inotify_inode_mark.fhandle at all? 
What prevents us from assembling this info on demand when ->show_fdinfo() is
called?


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