caching questions with jffs2

caching questions with jffs2

[Carlson, Kristen]

Hi,
Can someone describe to me the algorithm used for freeing memory that has
been cached due to file activity in jffs2?  Is this done as part of the
garbage collector?  How long does the cached memory stay around?  Is this
tunable?
Thanks,
Kristen Carlson

Re: caching questions with jffs2

[David Woodhouse]

kristen.carlson@intel.com said:
> Can someone describe to me the algorithm used for freeing memory that
> has been cached due to file activity in jffs2?  Is this done as part
> of the garbage collector?  How long does the cached memory stay
> around?  Is this tunable?

At all times while mounted, JFFS2 keeps a list of the offsets of each 
physical node belonging to each inode.

On read_inode(), it reads each physical node and builds up a full map of 
where data are found for each range of bytes in the file. 

On read(), it just reads data into the page cache. Normal Linux cache 
eviction rules apply to data pages.

On clear_inode(), the extra stuff allocated in read_inode() is freed.

The paper linked from http://sources.redhat.com/jffs2/ may help to shed 
light on this.

--
dwmw2