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

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Date:	Tue, 13 Nov 2012 15:02:22 +0000
From:	Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 Tuesday 13 November 2012 18:40:36 Cyrill Gorcunov wrote:
> On Tue, Nov 13, 2012 at 12:37:23PM +0000, Tvrtko Ursulin wrote:
> >> Which would give about 26K of additional memory if c/r get used here.
> >> 
> >>  Not a big number i guess?
> > 
> > I am pretty sure there are desktop file indexing packages which use
> > inotify or fanotify which will put a mark on every single directory within
> > users home.
> > 
> > You probably need to test this with default installs of popular desktop
> > environments and realistic home directories.
> 
> I'm about to shrink the handle down to 40/64 bytes as being proposed in one
> of early review cycles (i'll do that with patch on top), which should
> minimize the amount of memory needed (look, it's pretty clear that if the
> system uses millions of inotify watchers each inotify mark will need the
> fhandle here in c/r sake, i simply see no way at moment how to escape this

Well I spotted uncertainty in this thread about how many of these structures 
will typically be instantiated at runtime which is what I tried to add to this 
discussion. I have 60k directories in my home for example...

If you don't want to use information I provided that is your choice. Because 
you are still probably doubling this structure. Give or take - I haven't 
actually bothered counting.

Perhaps there could be a different way, where you could use additional space 
only when it is actually used at runtime. But as I said, I am not following 
closely.

> completely, but if the c/r is turned off, which is by default, no
> additional memory needed).

By turned on and off you are not talking about runtime but about kernel 
compile time, right? Do you envisage distributions turning this on, like they 
do for most things?

> p.s.: could you please don't use the html formatted messages

I thought I sent a multi-part message which had a plain text part as well. 
Granted this is not something I usually do, but on this occasion haven't 
completed configuring my email client after a configuration loss.

Regards,

Tvrtko

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