Hi all, Following was the discussion which i had on lkml. But still some doubts are there. So can anybody shed more light on it? ---------- Forwarded message ---------- From: yogeshwar sonawane <yogyas@xxxxxxxxx> Date: Feb 4, 2007 4:40 PM Subject: Re: Excessive printks increase top mem usage? To: davids@xxxxxxxxxxxxx Cc: linux-kernel <linux-kernel@xxxxxxxxxxxxxxx> cc to lkml On 2/3/07, yogeshwar sonawane <yogyas@xxxxxxxxx> wrote:
Thanks for the explanation. On 1/26/07, David Schwartz <davids@xxxxxxxxxxxxx> wrote: > > > On 1/25/07, yogeshwar sonawane <yogyas@xxxxxxxxx> 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 > > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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