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From Justin Erenkrantz <jerenkra...@ebuilt.com>
Subject Re: Buckets destroy not cleaning up private structures?
Date Mon, 30 Apr 2001 23:25:38 GMT
On Mon, Apr 30, 2001 at 03:20:17PM -0400, Cliff Woolley wrote:
> > How do we decide that?  Doesn't that depend on your OS and the size of
> > the MMAP extents (imagine 2 2GB files in your cache - which may be fine
> > on certain OSes but not on others - imagine 64bit address spaces).  That
> > is my inherent problem with using MMAP.
> 
> To be more precise, "too many MMAPs" is not just a factor of sheer number,
> it's (size1+size2+size3+...+sizen > OVERALL_MMAP_BYTES_LIMIT).  I just
> made that constant up, obviously, but apr_buckets_file.c defines
> MMAP_LIMIT for its own purposes (if it's not already defined, that is), so
> I see no reason that mod_file_cache couldn't similarly define a global
> limit in the same vein.
> 
> The file buckets code has a default MMAP_LIMIT for a given file of 4MB,
> just to give you an idea.  Any file bigger than that won't get MMAPed in
> the first place, at least not by the buckets code.  Multiply that times
> some sane number of files you wish to have MMAPed at one time, and voila,
> you've got your global limit for mod_file_cache.
> 
> Right?

Correct, but wouldn't it be "fairly" expensive to calculate how much 
space you have allocated with MMAP?  Or, you try and keep a static 
"cached" value of how much space you've allocated.  I bet this might be
a good place to use a reader/writer lock (wonder if anyone has 
implemented that - <G>).  -- justin


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