Re: [CFT][PATCH] Re: Fwd: Re: memory usage - dentry_cache

Alexander Viro
2001-04-12T13:54:44Z

On Thu, 12 Apr 2001, Marcin Kowalski wrote:

> Hi
>
> Regarding the patch ....
>
> I don't have experience with the linux kernel internals but could this patch
> not lead to a run-loop condition as the only thing that can break our of the
> for(;;) loop is the tmp==&dentry_unused statement. So if the required number
> of dentries does not exist and this condition is not satisfied we would have
> an infinate loop... sorry if this is a silly question.

Nope. Notice that "warned" dentries are not killed, but they are returned
to the list. If we meet them again - they are goners.

More formally, on each iteration you either decrement count or you
decrement the number of dentries that have DCACHE_REFERENCED. count
can't grow at all. Number of dentries with DCACHE_REFERENCED can't grow
unless you release dcache_lock, which happens only in the branch that
decrements count. I.e. loop does terminate.

> Also the comment >/* If the dentry was recently referenced, don't free it.
> */<, the code inside is excuted if the DCACHE_REFERENCED flags are set and in
> the code is is reversing the DCACHE_REFERENCED flag on the dentry and adding
> it to the dentry_unsed list??? So a Refrenched entry is set Not Referenced
> and place in the unsed list?? I am unclear about that... is the comment
> correct or is my understanding lacking (which is very probable :-))..

"referenced" as in "had been found by d_lookup, don't shoot me at sight".
When prune_dcache() picks it up it moves the thing on the other end of list
and removes the mark. Caught twice - too bad, it will be freed.
Al