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

From: Tobin C. Harding
Date: Mon Mar 11 2019 - 21:48:46 EST


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