Cleancache

[dexen deVries <dexen.devries-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi list,


there's that recent interesting addition to linux: `cleancache' (and 
`zcache').
I've enabled it for NILFS2 yesterday (in 3.0-rc2).
It seemed to work for a while -- sensible numbers in 
/sys/kernel/mm/cleancache/* 
But it broke terribly after performing
echo 3 > /proc/sys/vm/drop_caches
kernel reported NULL pointer dereference, IIRC. Ext4 works a-OK with that, so 
my first guess waws NILFS2 is doing something funky with page allocation or 
mapping.

Cleancache has own hooks into VFS, and for `normal' filesystem that's enough; 
at least enough for ext3 and ext4 drivers to work reliably. On the other hand, 
btrfs does something unusual with pages and they used extra cleancache hooks 
for btrfs, IIRC.

Should I dig further, post backtraces or something?

I believe using cleancache + zcache could be beneficial, especially for NILFS2 
metadata like the DAT file; what are your thoughts on it?


Regards,
-- 
dexen deVries

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