Re: missing madvise functionality

[Eric Dumazet <dada1@cosmosbay.com>]

Nick Piggin a écrit :
> Eric Dumazet wrote:
> >> This was not a working patch, just to throw the idea, since the
>> answers I got showed I was not understood.
>>
>> In this case, find_extend_vma() should of course have one struct 
>> vm_area_cache * argument, like find_vma()
>>
>> One single cache on one mm is not scalable. oprofile badly hits it on 
>> a dual cpu config.
> 
> Oh, what sort of workload are you using to show this? The only reason 
> that I
> didn't submit my thread cache patches was that I didn't show a big enough
> improvement.
> 

Database workload, where the user multi threaded app is constantly accessing 
GBytes of data, so L2 cache hit is very small. If you want to oprofile it, 
with say a CPU_CLK_UNHALTED:5000 event, then find_vma() is in the top 5.

Each time oprofile has an NMI, it calls find_vma(EIP/RIP) and blows out the 
target process cache (usually plugged on the data vma containing user land 
futexes). Event with private futexes, it will probably be plugged on the brk() 
vma.