Re: [PATCH]: Option to run cache reap in thread mode

[Manfred Spraul]

Andrew Morton wrote:

> Dimitri Sivanich <sivanich@xxxxxxx> wrote:
>  
>
> > At the time of the holdoff (the point where we've spent a total of 30 usec in
> > the timer_interrupt), we've looped through more than 100 of the 131 caches,
> > usually closer to 120.
> >    
>
> ahh, ooh, ow, of course.
>
> Manfred, we need a separate list of "slabs which might need reaping".
>  
A cache that might need reaping is a cache that has seen at least one 
kmem_cache_free(). The list would trade less time in the timer context 
at the expense of slower kmem_cache_free calls. I'm fairly certain that 
this would be end up as a big net loss.

> That'll help the average case.  To help the worst case we should change
> cache_reap() to only reap (say) ten caches from the head of the new list
> and to then return.
I'll write something:
- allow to disable the DMA kmalloc caches for archs that do not need them.
- increase the timer frequency and scan only a few caches in each timer.
- perhaps a quicker test for cache_reap to notice that nothing needs to 
be done. Right now four tests are done (!flags & _NO_REAP, 
ac->touched==0, ac->avail != 0, global timer not yet expired). It's 
possible to skip some tests. e.g. move the _NO_REAP caches on a separate 
list, replace the time_after(.next_reap,jiffies) with a separate timer.

--
   Manfred
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