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

From: Roman Gushchin
Date: Mon Mar 11 2019 - 20:10:02 EST

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:
> 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.