Re: [RFC 00/15] mm: Implement Slab Movable Objects (SMO)

[Tobin C. Harding]

On Tue, Mar 12, 2019 at 12:09:31AM +0000, Roman Gushchin wrote:
> On Fri, Mar 08, 2019 at 03:14:11PM +1100, Tobin C. Harding wrote:
> > Hi,
> > 
> > Here is a patch set implementing movable objects within the SLUB
> > allocator.  This is work based on Christopher's patch set:
> > 
> >  https://lore.kernel.org/patchwork/project/lkml/list/?series=377335
> > 
> > The original code logic is from that set and implemented by Christopher.
> > Clean up, refactoring, documentation, and additional features by myself.
> > Blame for any bugs remaining falls solely with myself.  Patches using
> > Christopher's code use the Co-developed-by tag.
> > 
> > After movable objects are implemented a number of useful features become
> > possible.  Some of these are implemented in this series, including:
> > 
> >  - Cache defragmentation.	   
> > 
> >     Currently the SLUB allocator is susceptible to internal
> >     fragmentation.  This occurs when a large number of cached objects
> >     are allocated and then freed in an arbitrary order.  As the cache
> >     fragments the number of pages used by the partial slabs list
> >     increases.  This wastes memory.
> > 
> >     Patch set implements the machinery to facilitate conditional cache
> >     defragmentation (via kmem_cache_defrag()) and unconditional
> >     defragmentation (via kmem_cache_shrink()).  Various sysfs knobs are
> >     provided to interact with and configure this.
> > 
> >     Patch set implements movable objects and cache defragmentation for
> >     the XArray.
> > 
> >  - Moving objects to and from a specific NUMA node.
> > 
> >  - Balancing objects across all NUMA nodes.
> > 
> > We add a test module to facilitate playing around with movable objects
> > and a python test suite that uses the module.
> > 
> > Everything except the NUMA stuff was tested on bare metal, the NUMA
> > stuff was tested with Qemu NUMA emulation.
> > 
> > Possible further work:
> > 
> > 1. Implementing movable objects for the inode and dentry caches.
> > 
> > 2. Tying into the page migration and page defragmentation logic so that
> >    so far unmovable pages that are in the way of creating a contiguous
> >    block of memory will become movable.  This would mean checking for
> >    slab pages in the migration logic and calling slab to see if it can
> >    move the page by migrating all objects.
> 
> 
> Hi Tobin!
> 
> Very interesting and promising patchset! Looking forward for inode/dentry
> moving support, might be a big deal for allocating huge pages dynamically.

Thanks Roman, appreciate the support.  I'm working on inode and dentry
now.

	Tobin