Re: kmalloc in the schedule function

[anil dahiya <ak_ait@xxxxxxxxx>]

Hi

on 2.4.21-32(redhat enterprise update 5) when i call kmalloc  with GFP_KERNEL 

my system get hangs it hangs.. Anyone can suggest what should i do ..

 

-- Anil

 

Hareesh Nagarajan <hnagar2@xxxxxxxxx> wrote:

On 3/9/06, Mauricio Lin wrote:
> Hi all,
>
> Is it possible to use kmalloc() in schedule() function?
>
> I have used kmalloc to allocate memory in schedule() but it does not work
> since during the boot the kernel gets frozen.

kmalloc with the flag GFP_KERNEL can potentially sleep. Which means,
the resource, which in this case is memory, cannot be allocated in an
atomic manner, so the kernel can put the requester in a wait queue,
call schedule(). (and of course when the resource is available, the
requester is woken up.)

So now inside schedule() you have a call that can sleep, or in other
words, you have a call that can schedule(). So you see:

schedule()
kmalloc(...)
schedule()
kmalloc(...)
...

This is far from ideal. You will run out of stack, which inside the
kernel is only 4K. Stay away from kmalloc-ing inside schedule, or if
you really need to use kmalloc, use it with the flag GFP_ATOMIC.

--
c u
./hareesh

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