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Thu, 09 Jul 2026 10:51:19 -0700 (PDT) Date: Thu, 9 Jul 2026 13:51:19 -0400 From: Johannes Weiner To: Shakeel Butt Cc: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/4] mm: fix reclaim storms in defrag_mode Message-ID: References: <20260626182215.1107966-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 575F74000C X-Stat-Signature: ohsijgdmocdm8egkii8icxmwtbpewuu4 X-HE-Tag: 1783619482-236430 X-HE-Meta: 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 BanxgaIz qpId+Vi5OQpRY01WrFQWJ2A1tgsliv0tyE6HjL1zeNUwrvNuYjpRjCwCxsNpE3UaAdb0rGsQdEj+ZrJmxfxJQBwhhJlZUiq+dIrECeTR3SV+s89cylzRK8CQXGc+K78gO61qF989av8rElmFcTHy1ZPXgORZQsaYRURZS/xJ83dgzmXgW8yCZeIvy9ep6JtAxqbhtkHUDJWc6bhllomXafGSpcNYvXaYJmMtjcgXUhtBqAsh9ilS3pFDJF6/8wbTMRutLRDXLknpOuS4LJutsfhglerQvzzEFLUJXCPn8YMg/Bq4se1ta2ar5ZTcVe5cC53rn2WYNTn/V/1W4XswRD6FEy5+ZMhCQz54rXBBcg46EmgzHH8Yu8rZX2bhXjOmCwOMXvXiVT+7oZEYaebBTPaSTahiehE87lpEhYjh62jN62U61Ewj5XtJNH0yAIsNMBMfZQOVzVHXH2Lo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 01, 2026 at 05:31:11PM -0700, Shakeel Butt wrote: > 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 ^^^ non-movable requests :) > > 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? Kind of. The crux is that defrag_mode enforces ALLOC_NOFRAGMENT in the slowpath as well (whereas vanilla just does it in the fastpath). So it's documented to the extent that ALLOC_NOFRAGMENT is. > > 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). Let me add: [...] - meaning, they will invoke direct reclaim and direct compaction with pageblock_order. Does that clarify it a bit?