Paging of Kernel Memory
ashish anand
ashishanand26cs at gmail.com
Tue Sep 6 22:44:08 EDT 2011
Hi
on wed 7th sep Christopher Harvey wrote
>>It means that it can't be swapped to your swap partition, even if
>>you're not using it.
this thing I understood it pretty well but what about the line
"Therefore, every byte of
memory you consume is one less byte of available physical memory".What is
the meaning of this line and why it is so.
On Tue, Sep 6, 2011 at 9:30 PM, <kernelnewbies-request at kernelnewbies.org>wrote:
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> Today's Topics:
>
> 1. Re: Re: Regarding threaded irq and normal irq (anish singh)
> 2. CRC calculation in Module.symvers (Shakthi Kannan)
> 3. Re: Finding physical and logical core number in a kernel
> module ? (Alexandre Courbot)
> 4. How to identify Connected USB Storage device (Harddisk, flash
> Memory or SSD) (mani)
> 5. Paging of Kernel Memory (Vijay Chauhan)
> 6. Re: Paging of Kernel Memory (Christopher Harvey)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 6 Sep 2011 13:57:22 +0530
> From: anish singh <anish198519851985 at gmail.com>
> Subject: Re: Re: Regarding threaded irq and normal irq
> To: Mulyadi Santosa <mulyadi.santosa at gmail.com>
> Cc: Greg KH <greg at kroah.com>, tglx at linutronix.de, sandeep kumar
> <coolsandyforyou at gmail.com>, kernelnewbies at kernelnewbies.org
> Message-ID:
> <CAK7N6voUN+b8nj=nQNoU1wGVr=b9jCm+0Q43eHg7bPLcgB4Nzw at mail.gmail.com
> >
> Content-Type: text/plain; charset=UTF-8
>
> On Tue, Sep 6, 2011 at 10:59 AM, anish singh
> <anish198519851985 at gmail.com> wrote:
> > On Tue, Sep 6, 2011 at 10:51 AM, Mulyadi Santosa
> > <mulyadi.santosa at gmail.com> wrote:
> >> Hi :)
> >>
> >> On 06/09/2011, sandeep kumar <coolsandyforyou at gmail.com> wrote:
> >>> Hmm..But when i tried to take a mutex lock in threaded_irq, it is
> throwing a
> >>> warning message
> >>> "BUG: sleeping function called from invalid context"... So i was
> wondering
> >>> which way it is..
> >>
> >> Please don't top post :)
> >>
> >> Anyway, regarding that "BUG:" message, could it be that mutex function
> >> mistakenly assume it's called inside top half, thus bails out since
> > How can mutex assume? IMHO the message would have printed
> > because sleeping would be forbidden there but again AFAIK in the threaded
> > handler we can do I2C transactions which can sleep.So kind of
> > paradox there.
>
> >>something like using in_irq() inside the threaded irq handler?
> I think after going thorough the code of mutex_lock we can find out the
> reason why it is printing the warning eventhough we are calling it in a
> threaded handler i.e. kernel thread.
>
> >From the code:
> 126 /**
> 127 * might_sleep - annotation for functions that can sleep
> 128 *
> 129 * this macro will print a stack trace if it is executed in an atomic
> 130 * context (spinlock, irq-handler, ...).
>
> 129 line no is important.
> This might_sleep is called by mutex_lock function and in the defintion
> of __might_sleep i found below code.I think this below if condition is
> false because irqs_disabled is true.This causes the warning.
>
> if ((preempt_count_equals(preempt_offset) && !irqs_disabled()) ||
> system_state != SYSTEM_RUNNING || oops_in_progress)
> return;
>
> Hope i am right?
>
> > ps:I have seen the code where sandeep is doing the taking the mutex lock.
> > He is taking mutex lock at the beginging of the handler and releasing
> > at the end.
> >> sleeping is forbidden there? which mutex function do you use? (sorry I
> >> don't follow every locking functions exist now)
> >>
> >> --
> >> regards,
> >>
> >> Mulyadi Santosa
> >> Freelance Linux trainer and consultant
> >>
> >> blog: the-hydra.blogspot.com
> >> training: mulyaditraining.blogspot.com
> >>
> >> _______________________________________________
> >> Kernelnewbies mailing list
> >> Kernelnewbies at kernelnewbies.org
> >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >>
> >
>
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 6 Sep 2011 12:41:24 +0530
> From: Shakthi Kannan <shakthimaan at gmail.com>
> Subject: CRC calculation in Module.symvers
> To: kernelnewbies at kernelnewbies.org
> Message-ID:
> <CABG-yt2W02ToqJJ=-n773Lg-JCRnDYc7qzA0HsCw+morgnSx8Q at mail.gmail.com
> >
> Content-Type: text/plain; charset=UTF-8
>
> Greetings!
>
> I would like to know as to:
>
> 1. How the CRC is computed for an exported symbol in the Linux kernel, and
> 2. Given a kernel .c file, how can I obtain the CRC checksums for a symbol.
>
> For linux-3.0.2 (example), I compiled with CONFIG_MODVERSIONS=y, and
> running make built vmlinux, and generated the Module.symvers file. I
> believe genksyms is used to generate the CRC information.
>
> I had referred the "Kernel Symbols and CONFIG_MODVERSIONS"
> documentation [1] written by Mark McLoughlin. I tried the following in
> the top-level kernel sources:
>
> $ gcc -E -D__GENKSYMS__ -DCONFIG_MODVERSIONS -DEXPORT_SYMTAB
> crypto/api.c -I/tmp/linux-3.0.2/include
> -I/tmp/linux-3.0.2/arch/x86/include | ./scripts/genksyms/genksyms
>
> and I get the following error output:
>
> === Output ===
>
> /tmp/linux-3.0.2/include/linux/jiffies.h:43:42: error: division by zero in
> #if
> In file included from /tmp/linux-3.0.2/include/linux/tracepoint.h:19:0,
> from /tmp/linux-3.0.2/include/linux/module.h:18,
> from crypto/api.c:22:
> /tmp/linux-3.0.2/include/linux/rcupdate.h:160:2: error: #error
> "Unknown RCU implementation specified to kernel configuration"
> In file included from /tmp/linux-3.0.2/include/linux/module.h:21:0,
> from crypto/api.c:22:
> /tmp/linux-3.0.2/arch/x86/include/asm/module.h:59:2: error: #error
> unknown processor family
>
> === End ===
>
> The documentation for genksyms is old, and now there is no -k option?
>
> Appreciate any inputs in this regard,
>
> Thanks!
>
> SK
>
> [1] Kernel Symbols and CONFIG_MODVERSIONS.
> http://www.skynet.ie/~mark/pub/symbols.txt
>
> --
> Shakthi Kannan
> http://www.shakthimaan.com
>
>
>
> ------------------------------
>
> Message: 3
> Date: Tue, 6 Sep 2011 16:14:19 +0900
> From: Alexandre Courbot <gnurou at gmail.com>
> Subject: Re: Finding physical and logical core number in a kernel
> module ?
> To: Vaibhav Jain <vjoss197 at gmail.com>
> Cc: kernelnewbies at kernelnewbies.org
> Message-ID:
> <CAAVeFu+h9=-roQcJaoh_d4XNbm8BtqtbQRR7qrWgx0B-k27dHA at mail.gmail.com
> >
> Content-Type: text/plain; charset=UTF-8
>
> > I agree that the kernel module is not restricted to any core but is it
> > possible that whenever it is executed
> > it gives the core number whichever is executing it ?
>
> Have a look at the end of include/linux/smp.h: smp_processor_id()
> gives you the number of the current executing CPU. get_cpu() will do
> the same and will also disable preemption so that you will stay on
> that CPU until put_cpu() is called.
>
> >From user-space, you can use sched_getcpu() to obtain the same
> information.
>
> Hope this helps,
> Alex.
>
>
>
> ------------------------------
>
> Message: 4
> Date: Tue, 6 Sep 2011 16:02:33 +0530
> From: mani <manishrma at gmail.com>
> Subject: How to identify Connected USB Storage device (Harddisk, flash
> Memory or SSD)
> To: kernelnewbies at kernelnewbies.org
> Message-ID:
> <CAB+TZU93_edNTfbNVKvQdgWiJxDTNHWWunNT6VNbHP+=RTixfw at mail.gmail.com
> >
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi all,
>
> Is there any way to find out the type of the connected USB disk (Hard
> disk/SDD)?
>
> AFAIK there is a significant performance difference in Harddisk/SDD
> devices.
>
> Previously i though that the rotational flag in the sysfs will distinguish
> them but it is same for both the types
>
> #cat /sys/block/sda/queue/rotational
> 1 for both flash & HDD
>
> Is there any way to distinguish the USB Harddisk or SDD drives ?
>
> Thanks & Regards,
> Manish
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> ------------------------------
>
> Message: 5
> Date: Tue, 6 Sep 2011 17:48:12 +0530
> From: Vijay Chauhan <kernel.vijay at gmail.com>
> Subject: Paging of Kernel Memory
> To: kernelnewbies at kernelnewbies.org
> Message-ID:
> <CAJ61zBDd4tH7jn2YEpDSmbaTXODUqpjOKanPsk0sqgHbKyek8w at mail.gmail.com
> >
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
>
> i was going through the Linux Kernel Development book. It mention the
> following:
>
> "Additionally, kernel memory is not pageable.Therefore, every byte of
> memory you consume is one less byte of available physical memory."
>
> What is the meaning of 'Kernel memory is not pageable'? Anyone can
> give details would help me in understanding.
>
> Thanks,
> Vijay
>
>
>
> ------------------------------
>
> Message: 6
> Date: Tue, 06 Sep 2011 09:38:26 -0500
> From: Christopher Harvey <chris at basementcode.com>
> Subject: Re: Paging of Kernel Memory
> To: <kernelnewbies at kernelnewbies.org>
> Message-ID: <1d7f4b0da950c823cb12c54a4d555234 at basementcode.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On Tue, 6 Sep 2011 17:48:12 +0530, Vijay Chauhan wrote:
> > Hi,
> >
> > i was going through the Linux Kernel Development book. It mention the
> > following:
> >
> > "Additionally, kernel memory is not pageable.Therefore, every byte of
> > memory you consume is one less byte of available physical memory."
> >
> > What is the meaning of 'Kernel memory is not pageable'? Anyone can
> > give details would help me in understanding.
> >
> > Thanks,
> > Vijay
> >
> It means that it can't be swapped to your swap partition, even if
> you're not using it.
>
>
>
> ------------------------------
>
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