Re: kmem-pool-uvm

[Lars Heidieker <lars%heidieker.de@localhost>]

On 11/03/2011 02:02 AM, Mindaugas Rasiukevicius wrote:
> Hello Lars,
> 
> Sorry for late reply.
> 
> Lars Heidieker <lars%heidieker.de@localhost> wrote:
>>>> i uploaded a new version of the kmem-pool-vmem-uvm patch: 
>>>> ftp://ftp.netbsd.org/pub/NetBSD/misc/para/kmem-pool-vmem-uvm.patch
>>>>
>> <...>
>>
>> I've uploaded a new Version of the patch and a small patch that
>> replaces malloc with kmem in the ufs/ext2 (mainly) readdir code as
>> those allocation were (due to blocksize) 4k which made them just too
>> large with the malloc-header for the max 4k caches currently
>> implemented in the patch.
> 
> Thanks, I think the changes in essence are great and we should have
> them for netbsd-6.  Few comments:
> 
> - Having IPL_VM lock for kmem(9) can increase masking of interrupts and
>   given that we want to reduce allocations from the interrupt context,
>   it is not really desirable.  However, there is a long way to go and at
>   this point I think it is not a problem, since kmem cache layer will
>   minimise the use of the lock.
> 
> - As already said, in the long term we want to minimise memory allocations
>   from the interrupt context.  With kmem(9) becoming interrupt-safe, there
>   is a potential for abuse.  I think that the general purpose kmem_alloc(9)
>   and kmem_free(9) routines should explicitly prohibit calls from interrupt
>   context by keeping the asserts on !cpu_intr_p() and !cpu_softintr_p().
>   For this purpose, there can be e.g. kmem_intr_alloc()/kmem_intr_free(),
>   so we would have strict interface level separation preventing for abuse.
>   It would also be easier to find such allocations from interrupt-context.
> 
> - I would leave uvm_km_alloc/free() interface naming as is and instead of
>   heap_va_arena would have something similar to old, e.g. kmem_va_arena.
>   Also, perhaps s/heap_meta_arena/kmem_va_meta_arena/.
> 
> - From bt_refillglobal:
> 
> +       if (vmem_alloc(heap_meta_arena, PAGE_SIZE,
> +           (flags & ~VM_FITMASK) | VM_INSTANTFIT | VM_POPULATING, &va) != 0) 
> { 
> +               return ENOMEM;
> +       }    
> 
> Error path leaks vmem_btag_lock.
> 

I've uploaded a new version of the kmem-pool-vmem-uvm patch:
ftp://ftp.netbsd.org/pub/NetBSD/misc/para/kmem-pool-vmem-uvm.patch
It incorporates some enhancements and makes the talked about interrupt
safe version private to malloc(9) and fixes the leakage of vmem_btag_lock.

Lars

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