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Re: Is JFFS a full featured filesystem?



On Wed, 2 Aug 2000, David Woodhouse wrote:

> 
> alex@xxxxxxx.se said:
> >  Exactly how did you plan to work out the dirty ranges? Compare with
> > on-flash contents? 
> 
> Apparently it's easy when using generic_file_write, because prepare_write 
> will give you the exact range. 

Ok. I'll have to look at that some day.
 
> When doing writable mmap() we have to do something cleverer - basically yes,
> comparing with the on-flash contents. We can either do that by going and
> reading the flash nodes again on writepage(), or we can keep a copy of the 
> clean page in RAM before it's dirtied. 

I vote for comparing with on-flash content. Keeping the memory
requirements down is important for embedded systems low on memory.
 
> To start with, I'm inclined just to accept the hit of the 4Kb writes, and 
> let the GC combine nodes later as necessary. Comparing with old contents 
> can come later. This is only going to be a problem with writable mmap(), 
> which isn't supported at the moment _anyway_. The normal write() case is 
> fairly simple to optimise.

I agree. The current performance could easily be kept for files that just 
grow, and generic mmap writes in a file is pretty unusual.

/ Alex