Re: [PATCH 2/2] move slab pages to the lru, for 2.5.27

[Ed Tomlinson <tomlins@cam.org>]

On July 21, 2002 07:24 am, Craig Kulesa wrote:

> This patch is intermediate between where we were (freeing slab caches
> blindly and not in tune with the rest of the VM), and where we want to be
> (cache pruning by page as we scan the active list looking for cold pages
> to deactivate).  Uhhh, well, I *think* that's where we want to be.  :)
>
> How do we get there?
>
> Given a slab page, I can find out what cachep and slab I'm dealing with
> (via GET_PAGE_SLAB and friends).  If the cache is prunable one,
> cachep->pruner tells me what kind of callback (dcache/inode/dquot) I
> should invoke to prune the page.  No problem.
>
> The trouble comes when we try to replace shrink_dcache_memory() and
> friends with slab-aware pruners.  Namely, how to teach those
> inode/dcache/dquot callbacks to free objects belonging to a *specified*
> page or slab?  If I have a dentry slab, I'd like to try to liberate
> *those* dentries, not some random ones like shrink_dcache_memory does now.

Well not quite random.  It prunes the oldest entries.  The idea behind the prunable
callback is that some caches have specific aging methods.   What I tried to do here
was keep the rate of aging in sync with the VM.  

> I'm still trying to figure out how to make that work.  Or is that
> totally the wrong approach?  Thoughts?  ;)

Thats a question I have asked myself too.  What could be done is,  scan the 
entries in the slab encountered, using a call back, free them if they are purgeable.
If this ends up producing an empty slab, release it.

>Intermezzo has a funky dentry cache that may need a pruner method (??), 
>but I didn't touch it.  If there was a better way to do this, I was too 
>blind to see it.  

Looking at the Intermezzo dcache code, I think you made the right choise.
I do not think this needs a pruner method.

Ed Tomlinson