Re: what is the difference between kmalloc and vmalloc?
Hi... On Mon, Nov 26, 2012 at 1:51 PM, Vijay Chauhan wrote: > Is it necessary that vmalloc always allocate virtually contiguous > memory and not physically contiguous? to the best I know, yes vmalloc allocate virtually contigous. However, since they manage the pages by fiddling with the page tables, there is a chance that some of them are physically contigous IMHO > Except large size memory allocation why one needs to use vmalloc? Can > we say that use kmalloc and if it fails retry with kmalloc? nice question: AFAIK vmalloc() is made to tackle large size memory allocation, or in other word to side step memory fragmentation issue. IIRC too, that by using vmalloc, the vmalloc-ed area are guarded by guard pages on both start and end address. So it's like stack overflow guard pages. But don't count me on this info. Check it by yourself. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: what is the difference between kmalloc and vmalloc?
On Thu, Nov 22, 2012 at 9:39 AM, Mulyadi Santosa wrote: > On Thu, Nov 22, 2012 at 10:12 AM, horse_rivers wrote: >> thanks! > > kmalloc allocates memory from slab cache. It tends to be physically > contigous and you can get memory size smaller than page size. > > vmalloc, on the other hand, is when you need only virtually contigous > memory area. Example of such usage is for allocating memory to load > kernel module. Is it necessary that vmalloc always allocate virtually contiguous memory and not physically contiguous? Except large size memory allocation why one needs to use vmalloc? Can we say that use kmalloc and if it fails retry with kmalloc? regards Vijay > > -- > regards, > > Mulyadi Santosa > Freelance Linux trainer and consultant > > blog: the-hydra.blogspot.com > training: mulyaditraining.blogspot.com > > ___ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: what is the difference between kmalloc and vmalloc?
kmalloc allocates physically contiguous memory, while vmalloc allocates memory which is only virtually contiguous and not necessarily physically contiguous. Usually physically contiguous memory is required for hardware devices (dma etc) , thus kmalloc is useful for allocating such memory. And though this is not always the requirement, still kmalloc is preferred , because it is better in terms of performance, because vmalloc can result in greater TLB thrashing . vmalloc is useful when very large amounts of memory is to be allocated, because when memory becomes heavily fragmented, you may not get success while allocating large memory via kmalloc. Slab layer serves like a cache for commonly used data structures, again with a view to reduce fragmentation, and to speed up operations. To allocate objects from slab you will have to use functions like kmem_cache_create() and kmem_cache_alloc() .. thanks Vivek On Thu, Nov 22, 2012 at 8:42 AM, horse_rivers wrote: > > thanks! > > ___ > Kernelnewbies mailing list > Kernelnewbies@kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
Re: what is the difference between kmalloc and vmalloc?
On Thu, Nov 22, 2012 at 10:12 AM, horse_rivers wrote: > thanks! kmalloc allocates memory from slab cache. It tends to be physically contigous and you can get memory size smaller than page size. vmalloc, on the other hand, is when you need only virtually contigous memory area. Example of such usage is for allocating memory to load kernel module. -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
what is the difference between kmalloc and vmalloc?
thanks! ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
