[ros-kernel] Re: Cache and memory manager

[David W. <we...@cw...>]

On Sun, Oct 14, 2001 at 07:05:23PM -0400, Phillip Susi wrote:
> Who was it that recently did some work with the cache manager code?  Are 
> you still working on it?  The Cc code needs to be reworked to use mapped 
> section views like NT does instead of CACHE_SEGMENTs.  
>
No, it doesn't.

> Currently, trying to copy a file on a machine with 8 megs of ram causes the 
> cache to use all available memory, run out, and then the system locks 
> up.  This is due to several reasons, the first being that the cache 
> does not currently have any mechanism to prevent it from growing 
> without bound.  
>
Yes, but this shouldn't be very difficult to add.

> The cache needs to map views of the files to be cached into the cache 
> working set, and the working set and page fault handling code will keep 
> the cache working set from growing without bound, as well as reclaiming 
> cache memory.  
>
Why? For the cache we have exact LRU information.

> The other bug in the current code is in cc/view.c in 
> CcRosGetCacheSegment, which does this:
> 
>         Status = MmCreateVirtualMapping(NULL,
> 			      current->BaseAddress + (i * PAGESIZE),
> 			      PAGE_READWRITE,
> 			      (ULONG)MmAllocPage(0));
> 
> Note that the call to MmAllocPage is not checked for failure.  On my test 
> system, it fails when memory runs out, and returns 0, which then gets 
> passed to MmCreateVirtualMapping for the physical backing page.  If noone 
> is working on this, I guess I'll go for it, but if someone already is, let 
> me know.
> 
I'm working on adding support for balancing memory usage including from 
the cache.

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