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From Luke Kenneth Casson Leighton <l...@samba-tng.org>
Subject Re: Observations on fragmentation in SMS pools
Date Tue, 10 Jul 2001 14:57:25 GMT
On Sun, Jul 08, 2001 at 10:19:33AM -0700, Justin Erenkrantz wrote:
> On Sun, Jul 08, 2001 at 10:14:16AM -0700, dean gaudet wrote:
> > an ideal situation for free-lists (blocks of freed, but not free()d
> > memory) is one per cpu.
> > 
> > a less ideal situation is one per thread.
> > 
> > an even less ideal situation is one per process (which requires locking).
> > 
> > it's insane to have one per pool :)
> 
> I think we're shooting for #2 (less ideal).  Unless someone can come up
> with a way to dynamically tell how many CPUs we are running on and bind
> a free-list to a specific CPU.
> 
> We're currently doing #3 (even less ideal) in apr_pools.c.  
> 
> And, yeah, the current trivial SMS is doing #4.  =)  But, don't expect it 
> to stay like that.  And, if we implement the apr_sms_child_malloc, it
> gets to somewhere between #2 and #3.  -- justin

#5 the approach taken by tdb.  have a hash-chain.

then you get the best of all worlds.  simultaneous access
only requires that you lock *one* hash chain, which allows
a theoretical limit of number-of-hash-bucket simultaneous
accesses.

luke

p.s. i'm hoping that people will not be put off by tdb's GPL
license because i think that there are some really good techniques
used in there that could be applied to APR code, too.

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