Re: [Linux-ia64] kmalloc() size-limitation

Re: [Linux-ia64] kmalloc() size-limitation

[Jes Sorensen]

Christian Hildner <christian.hildner@hob.de> writes:

> David,
> 
> you proposed me to use alloc_pages() instead of kmalloc() in order
> to get memory bigger than the 128K limit of the kmalloc() call. But
> even driver-developers don't want to handle with the page struct
> unless this is unavoidable. Which are the disadvantages of
> increasing the size limit of kmalloc() to 256K, 512K or 1M since
> machines are getting bigger and 64Bit machines break with current
> memory limitations?

Because drivers needs to work on all architectures and relying on
different hahavior from kmalloc() is bad.

Jes

Re: [Linux-ia64] kmalloc() size-limitation

[Christian Hildner]

Jes Sorensen schrieb:

> Christian Hildner <christian.hildner@hob.de> writes:
>
> > David,
> >
> > you proposed me to use alloc_pages() instead of kmalloc() in order
> > to get memory bigger than the 128K limit of the kmalloc() call. But
> > even driver-developers don't want to handle with the page struct
> > unless this is unavoidable. Which are the disadvantages of
> > increasing the size limit of kmalloc() to 256K, 512K or 1M since
> > machines are getting bigger and 64Bit machines break with current
> > memory limitations?
>
> Because drivers needs to work on all architectures and relying on
> different hahavior from kmalloc() is bad.
>
> Jes

Jes,

sorry for being unclear. I mean from increasing the kmalloc() size-limit
all platforms would benefit.

Christian

PS: David, I am looking forward getting your book. You are doing a great
job.

Re: [Linux-ia64] kmalloc() size-limitation

[Jes Sorensen]

>>>>> "Christian" == Christian Hildner <christian.hildner@hob.de> writes:

Christian> Jes Sorensen schrieb:
>> Because drivers needs to work on all architectures and relying on
>> different hahavior from kmalloc() is bad.

Christian> sorry for being unclear. I mean from increasing the kmalloc()
Christian> size-limit all platforms would benefit.

Thats not really a good idea, and definately not something you want to
rely on. A lot of architectures are still stuck with 4KB pages and
trying to allocate 128KB on larger in one chunk is likely to fail after
the system has been running for a while. On an ia64 with 16KB or 64KB
pages it's fairly likely it will work, but this is not necessarily a
good idea to do for other archs. If you need such a large block of
memory, vmalloc() is the real way to go.

Jes

Re: [Linux-ia64] kmalloc() size-limitation

[Christian Hildner]

Jes Sorensen schrieb:

> >>>>> "Christian" == Christian Hildner <christian.hildner@hob.de> writes:
>
> Christian> Jes Sorensen schrieb:
> >> Because drivers needs to work on all architectures and relying on
> >> different hahavior from kmalloc() is bad.
>
> Christian> sorry for being unclear. I mean from increasing the kmalloc()
> Christian> size-limit all platforms would benefit.
>
> Thats not really a good idea, and definately not something you want to
> rely on. A lot of architectures are still stuck with 4KB pages and
> trying to allocate 128KB on larger in one chunk is likely to fail after
> the system has been running for a while. On an ia64 with 16KB or 64KB
> pages it's fairly likely it will work, but this is not necessarily a
> good idea to do for other archs. If you need such a large block of
> memory, vmalloc() is the real way to go.
>
> Jes

I think you are right. Memory fragmentation will become a real problem on
small machines.

Christian