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[109.81.26.156]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-435e1354205sm10054004f8f.41.2026.01.28.13.14.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 13:14:14 -0800 (PST) Date: Wed, 28 Jan 2026 22:14:13 +0100 From: Michal Hocko To: Gregory Price Cc: Akinobu Mita , linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, david@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, bingjiao@google.com Subject: Re: [PATCH v3 3/3] mm/vmscan: don't demote if there is not enough free memory in the lower memory tier Message-ID: References: <20260108101535.50696-1-akinobu.mita@gmail.com> <20260108101535.50696-4-akinobu.mita@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: jxisexsrpzf65rcfq1rbz6hby6s4p7tw X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DEE12C0010 X-HE-Tag: 1769634856-981946 X-HE-Meta: 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 /gflH3lf 1F0bJCRHsyipFDhhES72rk04IgH/ZHLRMB5DbUUiBvBZMtERJb76tWJawDIlAdOsmh527wSFLvF/wPWmdJmaJqma9BFqz5Ee0QRH0qLFbor5KUcATRCaF/selE8EvrUdS3ropmsECfKeVkMsiQeaPsJuZbELUEcUGuEbgC2FUdEI+r8cFpZwS827P2/rTIAsfbJWk5RlYkVacQW00ZRvzzkhOVMoLHr6PxNKlcubCFLHU0LeYB8DkPEIdTLtJwrQ9EIBs3/b/BBS97JUEwcyPOVQS1gj5S6a4oOlSNobxiMyLCzVM8qTB7suIeWDwc7s9hHlIDjmqsEjhn1jDDyqPpjnTv4Bmlq5ziyDk/7bquV89gOQajI5JviPdBTc7CsPoCM37MutjMl576AmbKGD4phZlSGNHnLUzWZKC66NYhsFiqMioX+1+GLwqdL+P+KSrRQ/B+lvfO5oRyoKywOkTQ9wy8gH3fZDOEc/s X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed 28-01-26 09:21:45, Gregory Price wrote: > On Wed, Jan 28, 2026 at 10:56:44AM +0100, Michal Hocko wrote: > > > .gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) | > > > __GFP_NOMEMALLOC | GFP_NOWAIT, > > > }; > > > > This will trigger kswapd so there will be background reclaim demoting > > from those lower tiers. > > > > given the node is full kswapd will be running, but the above line masks > ~__GFP_RECLAIM so it's not supposed to trigger either reclaim path. Yeah, my bad, I haven't looked carefully enough. > > > Any chance you are using hugetlb on this system? This looks like a > > > clear bug, but it may not be what you're experiencing. > > > > Hugetlb pages are not sitting on LRU lists so they are not participating > > in the demotion. > > > > I noted in the v4 thread (responded there too) this was the case. > https://lore.kernel.org/linux-mm/aXksUiwYGwad5JvC@gourry-fedora-PF4VCD3F/ > > But since then we found another path through this code that adds > reclaim back on as well - and i wouldn't be surprised to find more. > > the bigger issue is that this fix can cause inversions in transient > pressure situations - and in fact the current code will cause inversions > instead of waiting for reclaim to clear out lower nodes. > > The reality is this code probably needs a proper look and detangling. Agreed! > This has been on my back-burner for a while - i've wanted to sink the > actual demotion code into memory-tiers.c and provide something like: > > ... mt_demote_folios(src_nid, folio_list) > { > /* apply some demotion policy here */ > } > > ~Gregory -- Michal Hocko SUSE Labs