Re: [PATCH v3 3/4] limit nr_dentries per superblock

From: Pekka Enberg
Date: Mon Aug 15 2011 - 06:58:09 EST

Hi Dave,

On Mon, Aug 15, 2011 at 1:46 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> That's usage for the entire slab, though, and we don't have a dentry
> slab per superblock so I don't think that helps us. And with slab
> merging, I think that even if we did have a slab per superblock,
> they'd end up in the same slab context anyway, right?

You could add a flag to disable slab merging but there's no sane way
to fix the per-superblock thing in slab.

On Mon, Aug 15, 2011 at 1:46 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
> Ideally what we need is a slab, LRU and shrinkers all rolled into a
> single infrastructure handle so we can simply set them up per
> object, per context etc and not have to re-invent the wheel for
> every single slab cache/LRU/shrinker setup we have in the kernel.
> I've got a rough node-aware generic LRU/shrinker infrastructure
> prototype that is generic enough for most of the existing slab
> caches with shrinkers, but I haven't looked at what is needed to
> integrate it with the slab cache code. That's mainly because I don't
> like the idea of having to implement the same thing 3 times in 3
> different ways and debug them all before anyone would consider it
> for inclusion in the kernel.
> Once I've sorted out the select_parent() use-the-LRU-for-disposal
> abuse and have a patch set that survives a 'rm -rf *' operation,
> maybe we can then talk about what is needed to integrate stuff into
> the slab caches....

Well, now that I really understand what you're trying to do here, it's
probably best to keep slab as-is and implement "slab accounting" on
top of it.

You'd have something like you do now but in slightly more generic form:

struct kmem_accounted_cache {
struct kmem_cache *cache;
/* ... statistics... */

void *kmem_accounted_alloc(struct kmem_accounted_cache *c)
if (/* within limits */)
return kmem_cache_alloc(c->cache);

return NULL;

Does something like that make sense to you?

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