using kmalloc

using kmalloc

[chiranjeevi vaka]

Hi,

I am getting some problems with kmalloc. If I tried to
allocate more than certain memory then the system is
hanging while booting with the changed kernel. Can you
suggest me how to come out this situation. Can't I
allocate as much I want when I want to allocate in the
kernel. 


Thank you,
Chiranjeevi

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Re: using kmalloc

[Arnaldo Carvalho de Melo]

Em Tue, Mar 19, 2002 at 08:18:31AM -0800, chiranjeevi vaka escreveu:

> I am getting some problems with kmalloc. If I tried to allocate more than
> certain memory then the system is hanging while booting with the changed
> kernel. Can you suggest me how to come out this situation. Can't I allocate
> as much I want when I want to allocate in the kernel. 

try vmalloc, kmalloc is limited, AFAIK, to 128 KiB and even that is difficult
to get after some time.

- Arnaldo

Re: using kmalloc

[yodaiken]

On Tue, Mar 19, 2002 at 01:41:36PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Mar 19, 2002 at 08:18:31AM -0800, chiranjeevi vaka escreveu:
> 
> > I am getting some problems with kmalloc. If I tried to allocate more than
> > certain memory then the system is hanging while booting with the changed
> > kernel. Can you suggest me how to come out this situation. Can't I allocate
> > as much I want when I want to allocate in the kernel. 
> 
> try vmalloc, kmalloc is limited, AFAIK, to 128 KiB and even that is difficult
> to get after some time.

Apparently, kmalloc semantics changed at some point
so it does not ever return error.


-- 
---------------------------------------------------------
Victor Yodaiken 
Finite State Machine Labs: The RTLinux Company.
 www.fsmlabs.com  www.rtlinux.com

Re: using kmalloc

[chiranjeevi vaka]

Hi jim,
I am trying to get something around 600 to 1000 bytes
using kmalloc. This one is for some changes in TCP/IP
stack. I am trying to implement a new kernel data
structure in tcp layer. So can you suggest me what
functionality to use to come out of that hanging.


thanks. 
--- James Washer <washer@us.ibm.com> wrote:
> 
> How much memory are you trying to get?  Also.. is
> this for a module, or a
> builtin function/driver/whatever?
>  - jim
> 
> chiranjeevi vaka
> <cvaka_kernel@yahoo.com>@vger.kernel.org on
> 03/19/2002
> 08:18:31 AM
> 
> Sent by:    linux-kernel-owner@vger.kernel.org
> 
> 
> To:    linux-kernel@vger.kernel.org
> cc:
> Subject:    using kmalloc
> 
> 
> 
> Hi,
> 
> I am getting some problems with kmalloc. If I tried
> to
> allocate more than certain memory then the system is
> hanging while booting with the changed kernel. Can
> you
> suggest me how to come out this situation. Can't I
> allocate as much I want when I want to allocate in
> the
> kernel.
> 
> 
> Thank you,
> Chiranjeevi
> 
> __________________________________________________
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Re: using kmalloc

[Tommy Reynolds]

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Uttered "chiranjeevi vaka" <cvaka_kernel@yahoo.com>, spoke thus:

>  I am trying to get something around 600 to 1000 bytes
>  using kmalloc. This one is for some changes in TCP/IP
>  stack. I am trying to implement a new kernel data
>  structure in tcp layer. So can you suggest me what
>  functionality to use to come out of that hanging.

Be sure to use "kmalloc( 1000, GFP_ATOMIC )" if you don't want to block waiting
for the memory.  Check for a NULL result, because you might not be able to get
the memory.

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Re: using kmalloc

[Dan Maas]

> I am getting some problems with kmalloc. If I tried to
> allocate more than certain memory then the system is
> hanging while booting with the changed kernel. Can you
> suggest me how to come out this situation. Can't I
> allocate as much I want when I want to allocate in the
> kernel.

kmalloc() allocates physically-contiguous pages of memory. Due to
fragmentation, more than 64KB-128KB of contiguous pages might not be
available, and hence kmalloc() will fail.

To allocate more memory, use vmalloc(), which allocates and maps physically
disjoint pages into a virtually-contiguous region. Be careful when doing DMA
to a vmalloc() area, since it is not physically contiguous and exists only
in the kernel's virtual memory map... Also I believe vmalloc()ed memory is
only accessible from (the context of) the process in which it was allocated
(?).

Regards,
Dan

Re: using kmalloc

[Alan Cox]

> To allocate more memory, use vmalloc(), which allocates and maps physically
> disjoint pages into a virtually-contiguous region. Be careful when doing DMA
> to a vmalloc() area, since it is not physically contiguous and exists only
> in the kernel's virtual memory map... Also I believe vmalloc()ed memory is
> only accessible from (the context of) the process in which it was allocated
> (?).

vmalloc memory is accessible everywhere. You can't allocate it during 
interrupts or tasklets, and you will get deadlocks if you allocate it in the
write out path of a file system/disk driver.

Alan

Re: using kmalloc

[Jan Hudec]

> kmalloc() allocates physically-contiguous pages of memory. Due to
> fragmentation, more than 64KB-128KB of contiguous pages might not be
> available, and hence kmalloc() will fail.

kmalloc allocates from generic slab caches. They come in sizes of powers
of 2 from 32B to 128KiB. The largest has slabs 128KiB large (on i386 at least).
Pages are allocated via __get_free_pages, so they have to be continuous.

However if you allocate namy instances of some structure, it's best to create
a kmem cache and allocate via kmem_cache_alloc (since it does not round the
requested size up to a power of two).

--------------------------------------------------------------------------------
                  				- Jan Hudec `Bulb' <bulb@ucw.cz>