Re: Excessive printks increase top mem usage?

Re: Excessive printks increase top mem usage?

[yogeshwar sonawane]

Subject is updated

On 1/25/07, yogeshwar sonawane <yogyas@gmail.com> wrote:
> Hi all,
> I am running a user application which will just open/close my driver
> (simple one, empty functions with only printks) infinitely.
> A massive use of printk can slow down the system noticeably OR it can
> affect some time calculations.
> Apart from this, it was increasing top mem usage also. After closing
> the application, the memory consumption was not coming down(not
> freeing mem). Is this the expected behaviour? OR i am missing
> something?
>
> Can anybody help me in guiding the reason for this? Any help/links plz.
>
> Thanks in advance,
> Yogeshwar
>

RE: Excessive printks increase top mem usage?

[David Schwartz]

> On 1/25/07, yogeshwar sonawane <yogyas@gmail.com> wrote:
> > Hi all,
> > I am running a user application which will just open/close my driver
> > (simple one, empty functions with only printks) infinitely.
> > A massive use of printk can slow down the system noticeably OR it can
> > affect some time calculations.
> > Apart from this, it was increasing top mem usage also. After closing
> > the application, the memory consumption was not coming down(not
> > freeing mem). Is this the expected behaviour? OR i am missing
> > something?
> >
> > Can anybody help me in guiding the reason for this? Any help/links plz.
> >
> > Thanks in advance,
> > Yogeshwar

What does "increased top mem usage" mean? You have given no reason to
suggest that there's anything unusual about this.

Here's one theory: Some program is writing these kernel messages to a file.
Because some other process might come and read that file later, the kernel
keeps copies of the file data in memory.

The kernel sees no advantage in having memory free. Free memory is memory
that's not doing any good. Better to keep data in memory that might be
useful later. We can always free the memory later if (and only if) we have
something better to do with it.

DS

Re: Excessive printks increase top mem usage?

[yogeshwar sonawane]

cc to lkml

On 2/3/07, yogeshwar sonawane <yogyas@gmail.com> wrote:
> Thanks for the explanation.
>
> On 1/26/07, David Schwartz <davids@webmaster.com> wrote:
> >
> > > On 1/25/07, yogeshwar sonawane <yogyas@gmail.com> wrote:
> > > > Hi all,
> > > > I am running a user application which will just open/close my driver
> > > > (simple one, empty functions with only printks) infinitely.
> > > > A massive use of printk can slow down the system noticeably OR it can
> > > > affect some time calculations.
> > > > Apart from this, it was increasing top mem usage also. After closing
> > > > the application, the memory consumption was not coming down(not
> > > > freeing mem). Is this the expected behaviour? OR i am missing
> > > > something?
> > > >
> > > > Can anybody help me in guiding the reason for this? Any help/links plz.
> > > >
> > > > Thanks in advance,
> > > > Yogeshwar
> >
> > What does "increased top mem usage" mean? You have given no reason to
> > suggest that there's anything unusual about this.
> >
> > Here's one theory: Some program is writing these kernel messages to a file.
> > Because some other process might come and read that file later, the kernel
> > keeps copies of the file data in memory.
> >
> > The kernel sees no advantage in having memory free. Free memory is memory
> > that's not doing any good. Better to keep data in memory that might be
> > useful later. We can always free the memory later if (and only if) we have
> > something better to do with it.
>
> One more thing:-
> If i want to allocate physical memory using __get_free_pages, and
> there is no free mem available, then kernel will release mem used by
> file data & use it for my request. Is this correct?
> I just tried similar thing. My test machine has 4GB RAM. On my test
> machine, as explained in my previous mail, i was printing excessive
> messages. Due to this top was showing mem usage aroung 1.9GB. Then i
> tried allocation of 4MB phy mem(using __get_free_pages) iteratively
> till it fails. The allocation succeeded upto @ 4-1.9 GB. I thought
> that some mem from 1.9 GB will be released for phy mem allocation. But
> it didn't. Such runs were tried 3-4 times. But consistently it
> succeeded upto 4-1.9GB. So is this normal ?
>
> regards,
> Yogeshwar
>
> >
> > DS
> >
> >
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