linux-kernel - Re: [patch 1/6] procfs: Introduce sequential fdinfo engine

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Message-ID: <20131031105752.GB24809@moon>
Date:	Thu, 31 Oct 2013 14:57:52 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	James Bottomley <jbottomley@...allels.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Matthew Helsley <matt.helsley@...il.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Tvrtko Ursulin <tvrtko.ursulin@...lan.co.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 1/6] procfs: Introduce sequential fdinfo engine

On Thu, Oct 31, 2013 at 01:32:13PM +0300, Alexey Dobriyan wrote:
> On Wed, Oct 30, 2013 at 10:59 PM, Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> > At moment the fdinfo operations (ie the output from /proc/$pid/fdinfo/$fd)
> > are generating output in one pass, which makes useless memory pressue
> > if the reader/user provides a buffer with a small size.
> 
> cat(1) uses 64 KB buffer.
> The output doesn't exceed one page anyway.

Yes, good point. I probably need to update changelog (forgot that i'm using
single_open here). What if we meet a file with that big number of epoll
or say notifies assigned that the fdinfo won't fit a page? I didn't meet
such scenario yet, but I think it's possible?
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