linux-kernel - Re: Disabling in-memory write cache for x86-64 in Linux II

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Date:	Fri, 25 Oct 2013 21:40:13 +0200
From:	Diego Calleja <diegocg@...il.com>
To:	"Artem S. Tashkinov" <t.artem@...os.com>
Cc:	david@...g.hm, neilb@...e.de, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	axboe@...nel.dk, linux-mm@...ck.org
Subject: Re: Disabling in-memory write cache for x86-64 in Linux II

El Viernes, 25 de octubre de 2013 18:26:23 Artem S. Tashkinov escribió:
> Oct 25, 2013 05:26:45 PM, david wrote:
> >actually, I think the problem is more the impact of the huge write later
> >on.
> Exactly. And not being able to use applications which show you IO
> performance like Midnight Commander. You might prefer to use "cp -a" but I
> cannot imagine my life without being able to see the progress of a copying
> operation. With the current dirty cache there's no way to understand how
> you storage media actually behaves.

This is a problem I also have been suffering for a long time. It's not so much 
how much and when the systems syncs dirty data, but how unreponsive the 
desktop becomes when it happens (usually, with rsync + large files). Most 
programs become completely unreponsive, specially if they have a large memory 
consumption (ie. the browser). I need to pause rsync and wait until the 
systems writes out all dirty data if I want to do simple things like scrolling 
or do any action that uses I/O, otherwise I need to wait minutes.

I have 16 GB of RAM and excluding the browser (which usually uses about half 
of a GB) and KDE itself, there are no memory hogs, so it seem like it's 
something that shouldn't happen. I can understand that I/O operations are 
laggy when there is some other intensive I/O ongoing, but right now the system 
becomes completely unreponsive. If I am unlucky and Konsole also becomes 
unreponsive, I need to switch to a VT (which also takes time).

I haven't reported it before in part because I didn't know how to do it, "my 
browser stalls" is not a very useful description and I didn't know what kind 
of data I'm supposed to report.
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