On Fri, 8 Oct 1999, Alexander Viro wrote:
yep we knew about this problem ... it's not quite an easy hack though.
Putting the directory block cache (and symlink block cache) into the page
cache would be the preferred method - this would also clean up the code
alot i think.
More or less random comments/questions:
1) Is ext2_bread() vs. bread() separation in fs/ext2/* a first step to
that? (I.e. data blocks vs. inode/bitmap/indirect ones)
2) Sometime ago there was a pretty impressive patch excluding large part
of ext2_find_entry() (it caches the offset into dentry and invalidates it
if needed) and I have a code for cyclic lookups in a directory (cheap
hack, but it really speeds the things up for ls -l and friends). Both
would go nicely into this scheme.
3) We ought to switch from (bh+pointer) to (page+pointer) in namei.c.
4) I still think that indirect blocks may go into the page cache - that
would further simplify truncate(). OTOH the method used by BSD (indirect
block covering addresses from n to n+block_size*pointers_per_block gets
an address -n, double indirect block covering the area from n to n+...
gets -n-block_size, triple indirect - -n-2*block size) will be wasteful
for situations when block size is smaller than page.
yes, all these cleanups would be very nice to have. I'm not aware of any
rathole in that area - even those small steps we took in early 2.3 proved
how much cleaner things could get.
The memory usage point on low memory machines - i dont think it holds.
Small directories (well, even larger ones ...) will use 4k, but since the
2.0 kernel moved to the page cache small files already used up 4k as well,
and there are more small files than small directories. In the case of
indirect pointers the 2.3 page cache only needs the indirect pointer once,
then it can be deallocated by the cache if there is memory pressure -
while 2.2 needed the indirect pointer for every write(). So i suspect 2.4
might even do better on small-memory boxes than 2.2.
5) Who works on that? I would try to do the thing, but if there already is
some code I'ld like to look at it, indeed.
nobody AFAIK.
-- mingo
