Re: IOCache vs. block cache

Ingo Weinhold <[email protected]> wrote:
> I think eventually the block cache should be rewritten to be VMCache 
> based 
> with on-demand mapping of hot blocks, but for the time being a simpler 
> solution would be possible:

Since there is no pressure to release within the next weeks, why not 
take the time to start working on the real solution instead of wasting 
time with another work-around?
Tackling the real thing would be much more rewarding, at least :-)

[...]
> * The block cache would no longer exert any memory pressure.

Not entirely true; all blocks that are in-use, dirty or have ongoing 
transactions would still require extra memory. While that is not that 
much in comparison, it may still create noticeable memory pressure.

> The only disadvantage I see is the double caching for file content: 
> The 
> IOCache caches at device level, the file caches at file level.

While that is certainly "dumb", I don't think it will be that bad in 
the end, since using memory for caching unbalanced probably hurts the 
performance more, than only using half of the memory (depending on what 
you do).

Another small disadvantage would be that the system needs to do much 
more to resurrect the blocks from the IOCache than simply return them 
from memory. Although this probably doesn't hurt much with the limited 
unused blocks list.

Bye,
   Axel.



------------------------------------------------------------------------------
ThinkGeek and WIRED's GeekDad team up for the Ultimate 
GeekDad Father's Day Giveaway. ONE MASSIVE PRIZE to the 
lucky parental unit.  See the prize list and enter to win: 
http://p.sf.net/sfu/thinkgeek-promo