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On Sat, 6 Feb 1999, Linus Torvalds wrote:
>
>
> On Sat, 6 Feb 1999, Alexander Viro wrote:
> >
> > Because It's Done That Way (tm). The simplest way to fix it would
> > probably be switching to slabs instead of using raw pages.
>
> It used to use slabs, and memory usage was _horrible_.
>
> > Linus, do you have any objections against it? If it's OK for you
> > I'll roll a patch and submit it.
>
> We had it already for a short moment in the 2.1.x series, and it simply
> didn't work very well. It had all the slab problems with multi-page
> allocations, and inodes also have very hard-to-predict allocation
> lifetimes, so what happened was that when you allocated a lot of inodes,
> the pages were almost never freed back to the page pool, because there was
> often a few inodes holding things locked down anyway.
>
> It's a long time ago, but I essentially reverted it within a few releases
> because _I_ had problems with it (and that's on machines with plenty of
> memory).
>
> > Another question: we still have a race in rename() on UNIX
> > filsystems (d_invalidate() stuff).
>
> Remind me..
If rename() is going to overwrite an existing directory it should check
that it's empty and (obvious race prevention) nobody else uses it.
Current code does shrink_dcache_parent() on the victim and then checks
d_count. It is not enough, since we are leaving the victim hashed and
anybody can grab it while we are checking emptiness and start to mess
with it.
Proposed fix: instead of
if (new_dentry->d_count>1)
shrink_dcache_parent(new_dentry);
if (new_dentry->d_count>1)
fail with -EBUSY
check emptiness
...
...
...
d_move(old_dentry,new_dentry);
do
if (d_invalidate(new_dentry)<0)
fail with -EBUSY
need_rehash=1;
check emptiness
...
...
...
if (need_rehash)
d_rehash(new_dentry);
d_move(old_dentry,new_dentry);
That is, try to unhash the victim, say EBUSY if failed, remember to
rehash it before d_move(), do emptiness check (we are safe now), do the
rest of rename, rehash the victim if needed and do d_move().
This should be done for affs, ext2, minix, sysvfs, ufs and coda.
vfat already does exactly that. So there... It's about 6-7 changed lines
in each fs. I'm attaching the patch against 2.2.2-pre2. Apply if you think
that it's suitable for 2.2.early. Race is real, so...
Cheers,
Al
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