Re: JFFS2 mount time

[Artem Bityuckiy <dedekind@oktetlabs.ru>]

Hello Jarkko,

> I tried Ferenc's earlier mount time patch in August and the 52s mount
> time dropped then to 14s. If I understand right, inodes and dentries
> were then mixed in the erase block and the summary was for inodes
> only.  This shows reading dentries from semirandom places is
> expensive.
This is very good that direntries are distributed more or less uniformly 
in average.

> 
> Ferenc's latest patch put dentries on their own erase block in
> consecutive order.  Considering only the read efficiency from the
> media, reading consecutive, uncompressed, and unstripped dentries from
> a summary should cost no more than reading them from dedicated erase
> block.
> 
Definitely true - the second patch must be better than the first one. But
unfortunately, it hard to do this dinamically :-( Ferenc tried...

But in my proposition, we will also refer direntries in the summary - 
this is not the same as to read direntries from where they are placed, 
this is another thing, especially in case of NAND! There is difference 
(if we have NAND) - whether to read one 512 NAND page containing 
compressed information about 20-25 direntries or to read 20-25 
*different* NAND pages.

So, I think, new design will also better than the early Ferenc's patch :-)

-- 
Best regards, Artem B. Bityuckiy
Oktet Labs (St. Petersburg), Software Engineer.
+78124286709 (office) +79112449030 (mobile)
E-mail: dedekind@oktetlabs.ru, web: http://www.oktetlabs.ru