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Old 11-03-2004, 11:09 PM   #1
dtrusty
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Registered: Nov 2004
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Do any kernels support a multi-gigabyte buffer cache?


Hi,

I have a system with 4.5G of ram.

I noticed (using 'free') that the system buffer cache
was limited to about 820M.

The server will hold up to 12G of ram.

I use kernel 2.4.20-31.9bigmem.

Do any kernels support a multi-gigabyte buffer cache?

Thanks,

David
 
Old 11-04-2004, 01:34 AM   #2
foo_bar_foo
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Registered: Jun 2004
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hi,

as far as i know Linux will automatically try to uses ALL free ram for buffer cache, and automatically makes the cache smaller when programs need more memory.
but low usage was a problem with those older kernels
i would migrate to 2.6 kernel where lots of issues with highmem have been addressed
2.6 kernel supports larger pages up to 2/4M and page table entries can now exist in highmem
removing the old 1Gb constraint for pte's allowing better use of more memory
has larger table lookaside buffer that can actually stay cached because pte's are moved out of lowmem
and since buffer cache like you said is ultimately about block device reads the kernel you are using had to route all block device i/o through the first 1Gb kernel set aside one locked read at a time and then bounce to a highmem address.
newer kernel block device drivers support direct highmem DMA and more finer grained locking and i bet this will fix what you are seeing and speed you up alot. and eliminate that waste of memory.
 
  


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