Page fault in kernel code

[orca.chen@gmail.com (Miles MH Chen)]

Not exactly, vmalloc'ed addresses can generate page faults.

vmalloc'ed page entries live in kernel master page table, not in

every process' page table. When a vmalloc page fault occurs,

kernel simply copy the page table entry from master page table to
the current process' page table and fix the page fault.

MH

On Thu, Sep 11, 2014 at 8:03 PM, Leon Romanovsky <leon@leon.nu> wrote:

> On Wed, Sep 10, 2014 at 5:52 PM, Manavendra Nath Manav
> <mnm.kernel@gmail.com> wrote:
> >
> > On 10-Sep-2014 6:24 pm, <Valdis.Kletnieks@vt.edu> wrote:
> >>
> >> On Wed, 10 Sep 2014 14:45:23 +0530, Manavendra Nath Manav said:
> >>
> >> > But if the total RAM is limited (less than 896MB LOWMEM), for example
> as
> >> > in
> >> > embedded devices how the kernel code be kept in RAM all the time. Am I
> >> > correct to assume that the kernel pre-fetches all pages when entering
> >> > kernel mode from user mode?
> >>
> >> No, kernel code is loaded by your boot loader, and *it stays there*.
> >> Similarly,
> >> if you modprobe something, the kernel allocates the page, loads the
> code,
> >> and leaves it there.
> >>
> >> Particularly in embedded devices, where you know all the modules the
> >> kernel may
> >> need, it's common to just create a kernel with everything built in, no
> >> module
> >> support, and when the system boots, it loads into memory and never moves
> >> again.
> >>
> >
> > Linux kernel memory is not page-able, but memory allocated through
> vmalloc
> > can still cause page fault. How device drivers using vmalloc handle this?
> Pages allocated via vmalloc call won't generate page-faults.
>
> >
> >
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> >
>
>
>
> --
> Leon Romanovsky | Independent Linux Consultant
>         www.leon.nu | leon at leon.nu
>
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