Re: [PATCH v4 0/6] fs/dcache: Limit # of negative dentries

[Dave Chinner]

On Wed, Oct 11, 2017 at 04:47:05PM -0400, Waiman Long wrote:
> On 10/10/2017 06:54 PM, Andrew Morton wrote:
> > On Mon, 18 Sep 2017 14:20:28 -0400 Waiman Long <longman@xxxxxxxxxx> wrote:
> >
> >> A rogue application can potentially create a large number of negative
> >> dentries in the system consuming most of the memory available even if
> >> memory controller is enabled to limit memory usage. This can impact
> >> performance of other applications running on the system.
> > It does seem that under these circumstances it is pretty silly of us to
> > reclaim useful things in order to instantiate zillions of -ve dentries.
> 
> I am talking about a misbehaving program due to bug or an intentional
> rogue program.
> 
> >
> > Dentries are subject to kmemcg handling.  Does this not help avoid
> > "impacting performance of other applications"?
> 
> AFAIK, the dentry kmem_cache isn't memcg aware.

The dentry cache is most definitely is memcg aware. It (and teh
inode cache) were the primary targets for the memcg slab reclaim
infrastructure.

#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
# define SLAB_ACCOUNT           0x04000000UL    /* Account to memcg */
#else
# define SLAB_ACCOUNT           0x00000000UL
#endif

dcache_init():

        dentry_cache = KMEM_CACHE(dentry,
                SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT);


Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx