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From:   Roman Gushchin <guro@fb.com>
To:     "Tobin C. Harding" <tobin@kernel.org>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Christopher Lameter <cl@linux.com>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        Matthew Wilcox <willy@infradead.org>,
        Tycho Andersen <tycho@tycho.ws>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 00/15] mm: Implement Slab Movable Objects (SMO)
Thread-Topic: [RFC 00/15] mm: Implement Slab Movable Objects (SMO)
Thread-Index: AQHU1WWWNeCS+/ChkEynjyh1uhCoA6YHJOwA
Date:   Tue, 12 Mar 2019 00:09:31 +0000
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References: <20190308041426.16654-1-tobin@kernel.org>
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On Fri, Mar 08, 2019 at 03:14:11PM +1100, Tobin C. Harding wrote:
> Hi,
>=20
> Here is a patch set implementing movable objects within the SLUB
> allocator.  This is work based on Christopher's patch set:
>=20
>  https://lore.kernel.org/patchwork/project/lkml/list/?series=3D377335
>=20
> 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.
>=20
> After movable objects are implemented a number of useful features become
> possible.  Some of these are implemented in this series, including:
>=20
>  - Cache defragmentation.	  =20
>=20
>     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.
>=20
>     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.
>=20
>     Patch set implements movable objects and cache defragmentation for
>     the XArray.
>=20
>  - Moving objects to and from a specific NUMA node.
>=20
>  - Balancing objects across all NUMA nodes.
>=20
> We add a test module to facilitate playing around with movable objects
> and a python test suite that uses the module.
>=20
> Everything except the NUMA stuff was tested on bare metal, the NUMA
> stuff was tested with Qemu NUMA emulation.
>=20
> Possible further work:
>=20
> 1. Implementing movable objects for the inode and dentry caches.
>=20
> 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!