Mailinglist Archive: opensuse (982 mails)

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Re: [opensuse] disk cache
  • From: "Carlos E. R." <carlos.e.r@xxxxxxxxxxxx>
  • Date: Mon, 22 Sep 2014 13:18:19 +0200 (CEST)
  • Message-id: <alpine.LSU.2.11.1409221310160.6675@Telcontar.valinor>
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On Monday, 2014-09-22 at 12:50 +0400, Andrei Borzenkov wrote:
On Mon, Sep 22, 2014 at 12:10 PM, Bernhard Voelker <> wrote:
On 09/22/2014 09:20 AM, Andrei Borzenkov wrote:
On Mon, Sep 22, 2014 at 11:07 AM, Bernhard Voelker <> wrote:
On 09/22/2014 08:31 AM, Roger Oberholtzer wrote:

The cache seems to be filling up

That is GOOD!

It depends. It is good when cache is filled up with data waiting to be
read. It is bad when it is filled up with data waiting to be written
out to slow device.


Well, in that case, you'll have to wait for the data to be sync'ed to
disk anyway. ;-)


Yes, but currently single application is able to fill in RAM with
unwritten data, so that the whole system (every other application) has
to wait while data is drained. And that blocks not only write-out, but
also reading of data. Resulting in very long delays and non-responsive
system.

AHHHHH!!!!!!!

SO THAT'S WHY!!

That's why writing big files, or many files, to slow usb flash devices makes the entire system crawl!


So while every single application will never write faster, each
application could be more responsive with smaller amount of cached
data.

What Linux still lacks is rate-limiting of program writes to match
output device speed.


Can we limit, externally, the amount of cache an application can use?

Say I want to start a large file copy to usb stick, like a dd to create an usb installation media. How do I tell it not to use a big write cache?

Or a many file copy to a usb device, using, say, mc.


Or instead of limiting the cache per application, do so per device. If the usb is on /dev/sdh, limit the cache on /dev/sdh.


Is this possible at all?


- -- Cheers,
Carlos E. R.
(from 13.1 x86_64 "Bottle" at Telcontar)

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