Re: negative dentries wasting ram

[Andrea Arcangeli]

On Fri, May 24, 2002 at 02:00:36PM -0400, Alexander Viro wrote:
> 
> 
> On Fri, 24 May 2002, Andrea Arcangeli wrote:
> 
> > so why don't you also left a negative directory floating around, so you
> > know if you creat a file with such name you don't need to ->loopup the
> > lowlevel fs but you only need to destroy the negative directory and all
> > its leafs in-core-dcache? If you did the negative effect would become
> > more obvious, the d_unhash hides it except for the spooling workloads.
>  
> -ENOPARSE

instead of dropping the dentry for a directory after an rmdir you could
left it there as a negative entry, it would avoid you to ->lookup if
somebody creat() using the name of such ex-directory.

> 
> > of kmem_cache_reap, so we are as efficient as possible, but we don't
> > risk throwing away very useful cache, for more dubious caching effects
> > after an unlink/create-failure that currently have the side effect of
> > throwing away tons of worthwhile positive pagecache (and even triggering
> > swap false positives) in some workloads.
> 
> I might buy that argument if we didn't also leave around _unreferenced_
> inodes for minutes in the icache.  And _that_ is much stronger source of

I don't see it, at the last iput of an inode with i_nlink == 0 the inode
is freed immediatly, not like the dcache that is left floating around as
a negative one with no useful caching effects for most workloads.

> memory pressure, so if you want to balance the thing you need to start
> there.

Andrea