Messages in this thread | | | Date | Thu, 8 Nov 2012 17:15:36 +0000 | From | Christoph Lameter <> | Subject | Re: [PATCH v6 25/29] memcg/sl[au]b: shrink dead caches |
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On Wed, 7 Nov 2012, Andrew Morton wrote:
> What's up with kmem_cache_shrink? It's global and exported to modules > but its only external caller is some weird and hopelessly poorly > documented site down in drivers/acpi/osl.c. slab and slob implement > kmem_cache_shrink() *only* for acpi! wtf? Let's work out what acpi is > trying to actually do there, then do it properly, then killkillkill!
kmem_cache_shrink is also used internally. Its simply releasing unused cached objects.
> Secondly, as slab and slub (at least) have the ability to shed cached > memory, why aren't they hooked into the core cache-shinking machinery. > After all, it's called "shrink_slab"!
Because the core cache shrinking needs the slab caches to free up memory from inodes and dentries. We could call kmem_cache_shrink at the end of the shrink passes in vmscan. The price would be that the caches would have to be repopulated when new allocations occur. > > If we can fix all that up then I wonder whether this particular patch > needs to exist at all. If the kmem_cache is no longer used then we > can simply leave it floating around in memory and the regular cache > shrinking code out of shrink_slab() will clean up any remaining pages. > The kmem_cache itself can be reclaimed via another shrinker, if > necessary?
The kmem_cache can only be released if all its objects (used and unused) are released. kmem_cache_shrink drops the unused objects on some internal slab specific list. That may enable us to release the kmem_cache structure.
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