Re: Swappiness vs. mmap() and interactive response

Balbir Singh
2009-04-28T07:58:36Z

On Tue, Apr 28, 2009 at 1:18 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, 2009-04-28 at 14:35 +0900, KOSAKI Motohiro wrote:
>> (cc to linux-mm and Rik)
>>
>>
>> > Hi,
>> >
>> > So, I just set up Ubuntu Jaunty (using Linux 2.6.28) on a quad core phenom box,
>> > and then I did the following (with XFS over LVM):
>> >
>> > mv /500gig/of/data/on/disk/one /disk/two
>> >
>> > This quickly caused the system to. grind.. to... a.... complete..... halt.
>> > Basically every UI operation, including the mouse in Xorg, started experiencing
>> > multiple second lag and delays.  This made the system essentially unusable --
>> > for example, just flipping to the window where the "mv" command was running
>> > took 10 seconds on more than one occasion.  Basically a "click and get coffee"
>> > interface.
>>
>> I have some question and request.
>>
>> 1. please post your /proc/meminfo
>> 2. Do above copy make tons swap-out? IOW your disk read much faster than write?
>> 3. cache limitation of memcgroup solve this problem?
>> 4. Which disk have your /bin and /usr/bin?
>>
>
> FWIW I fundamentally object to 3 as being a solution.
>

memcgroup were not created to solve latency problems, but they do
isolate memory and if that helps latency, I don't see why that is a
problem. I don't think isolating applications that we think are not
important and interfere or consume more resources than desired is a
bad solution.

> I still think the idea of read-ahead driven drop-behind is a good one,
> alas last time we brought that up people thought differently.

I vaguely remember the patches, but can't recollect the details.

Balbir