Hi Coly

Thanks for you comments.
> Hi Junhui,
> This method is complicated IMHO. 
The main idea of this patch is:

                GC thread                                               
allocator thread
==>triggered by sectors_to_gc
   set ca->prepare_gc to GC_PREPARING
   to notify allocator thread to
   prepare for GC                                       ==>detect 
ca->prepare_gc is 
GC_PREPARING, fill the 
go to invalidate_buckets(),
==>waiting for allocator                                and fill free_inc queue 
   thread to prepare over                               reclaimable buckets, 
that, set ca->prepare_gc to
GC_PREPARED to notify GC
thread being prepared OK
==>detect ca->prepare_gc is
   prepared OK, set 
   ca->prepare_gc back to 
   GC_PREPARE_NONE, and continue GC

> Why not in bch_allocator_thread()
> simple call wake_up_gc(ca->set) after invalidate_buckets() ?
In this patch, GC is triggered by sectors_to_gc, and I/Os from front side
continue exist, so we notify allocator to pack the free_inc queue
full of buckets before GC, then we could have enough buckets for front side
I/Os during GC period.

Maybe the code is somewhat redundant, I will try to refactoring the code
in the next patch.

Tang Junhui                              

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