lkml.org 
[lkml]   [2016]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: clarify COMPACTION Kconfig text
On Tue, 23 Aug 2016, Michal Hocko wrote:

> From: Michal Hocko <mhocko@suse.com>
>
> The current wording of the COMPACTION Kconfig help text doesn't
> emphasise that disabling COMPACTION might cripple the page allocator
> which relies on the compaction quite heavily for high order requests and
> an unexpected OOM can happen with the lack of compaction. Make sure
> we are vocal about that.
>

Since when has this been an issue? I don't believe it has been an issue
in the past for any archs that don't use thp.

> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/Kconfig | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 78a23c5c302d..0dff2f05b6d1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -262,7 +262,14 @@ config COMPACTION
> select MIGRATION
> depends on MMU
> help
> - Allows the compaction of memory for the allocation of huge pages.
> + Compaction is the only memory management component to form
> + high order (larger physically contiguous) memory blocks
> + reliably. Page allocator relies on the compaction heavily and
> + the lack of the feature can lead to unexpected OOM killer
> + invocation for high order memory requests. You shouldnm't
> + disable this option unless there is really a strong reason for
> + it and then we are really interested to hear about that at
> + linux-mm@kvack.org.
>
> #
> # support for page migration

This seems to strongly suggest that all kernels should be built with
CONFIG_COMPACTION and its requirement, CONFIG_MIGRATION. Migration has a
dependency of NUMA or memory hot-remove (not all popular). Compaction can
defragment memory within single zone without reliance on NUMA.

This seems like a very bizarre requirement and I'm wondering where we
regressed from this thp-only behavior.

\
 
 \ /
  Last update: 2016-09-17 09:57    [W:0.087 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site