Re: [PATCH 0/4] mm: fix reclaim storms in defrag_mode

[Shakeel Butt <shakeel.butt@linux.dev>]

On Fri, Jun 26, 2026 at 02:21:16PM -0400, Johannes Weiner wrote:
> As we deployed vm.defrag_mode=1 into Meta production, some workloads
> regressed with recurring pressure spikes and swap storms (which in turn
> triggered userspace OOM rules on pressure and swap utilization levels).
> 
> Tracing pinned this to non-movable 

allocation?

> requests spinning and reclaiming
> unproductively when kswapd/kcompactd are overwhelmed. Direct reclaim
> predominantly frees up pages in movable blocks, but those requests
> cannot use that space under defrag_mode rules; 

Do we have these rules documented somewhere?

> and it is unlikely to
> free up whole blocks incidentally for __rmqueue_claim() to work.
> 
> This series fixes it by making non-movable requests participate in
> pageblock production in the allocator slowpath.

Sorry after reading above sentence I didn't get what those allocators will do
things differently after the series (I still have to go through the series).

> 
> That requires some small-ish adjustments up front in the allocator and
> the compaction code: three prep patches and the fix last.
> 
> The series has been in production against one of the affected workloads
> for two weeks and restores the OOM kill rate to !defrag_mode baseline.
> 
> Based on mm-new (2026-06-22).
> 
>  include/linux/compaction.h |  3 +-
>  mm/compaction.c            | 68 ++++++++++++++++++++++++--------------------
>  mm/internal.h              |  7 +++++
>  mm/page_alloc.c            | 59 ++++++++++++++++++++++++++++++------
>  4 files changed, 98 insertions(+), 39 deletions(-)
>