Re: [PATCH -mm 2/3] slab: zap kmem_cache_shrink return value

[Vladimir Davydov <vdavydov@parallels.com>]

On Mon, Jan 26, 2015 at 02:28:33PM -0600, Christoph Lameter wrote:
> On Mon, 26 Jan 2015, Vladimir Davydov wrote:
> 
> > Right, but I just don't see why a subsystem using a kmem_cache would
> > need to check whether there are any objects left in the cache. I mean,
> > it should somehow keep track of the objects it's allocated anyway, e.g.
> > by linking them in a list. That means it must already have a way to
> > check if it is safe to destroy its cache or not.
> 
> The acpi subsystem did that at some point.
> 
> > Suppose we leave the return value as is. A subsystem, right before going
> > to destroy a cache, calls kmem_cache_shrink, which returns 1 (slab is
> > not empty). What is it supposed to do then?
> 
> That is up to the subsystem. If it has a means of tracking down the
> missing object then it can deal with it. If not then it cannot shutdown
> the cache and do a proper recovery action.

Hmm, we could make kmem_cache_destroy return EBUSY for the purpose.
However, since it spits warnings on failure, which is reasonable, we
have this check in kmem_cache_shrink...

Anyways, I see your point now, thank you for pointing it out. I will fix
SLUB's __kmem_cache_shrink retval instead of removing it altogether in
the next iteration.

Thanks,
Vladimir