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

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Date:	Tue, 13 Nov 2012 12:00:32 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Andrew Morton <akpm@...ux-foundation.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 Mon, Nov 12, 2012 at 11:40:01PM -0800, Andrew Morton wrote:
> On Tue, 13 Nov 2012 11:20:57 +0400 Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> > > 
> > > 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?

Well, hard to tell, to be fair. On my testing machine only apache has been
using inotify system as far as I remember, but for sure nothing except memory
limit the number of inotify. But I think if one running machine with millions
of inotify it's rather powerful machine with enough memory.

> 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?

exportfs requires the dentry to be passed as an argument while inotify works
with inodes instead and at moment of show-fdinfo the target dentry might be
already deleted but inode yet present as far as I remember.
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