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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8b5299a5d48sm1251362685a.12.2025.12.03.00.59.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Dec 2025 00:59:51 -0800 (PST) Date: Wed, 3 Dec 2025 03:59:50 -0500 From: Gregory Price To: Michal Hocko Cc: Andrew Morton , Aboorva Devarajan , vbabka@suse.cz, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador , David Hildenbrand Subject: Re: [PATCH] mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free Message-ID: References: <20251201060009.1420792-1-aboorvad@linux.ibm.com> <20251201094112.07eb1e588b6da2ee70c4641d@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 07FD620006 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: ujpqyb9rc6cxtuuogjyfyfozznqse5az X-HE-Tag: 1764752392-344945 X-HE-Meta: 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 upGBir5k XBWwsRSaN0hVr36QPYL+91lMCiWCYYcBu6y1Q3jn7tKIqk3pqSCmronrkd881hz+6fBRgM+FbG8g7sgHti7NOoJpBf0GrUmO1kaqOTXKfp2IqAK8zfDJONIynQds/dmOjKi0LFY0T42yTlmkdvdMBw677lwnIe5tPO1QC6gzlIRIWiZni2ExA1NGPFDRzz/ooSef3kjERQDpRgQAM9AgDuL3ZfH8p+zjvp/kP3fMgd3AMiYLNvvobVtgPlTmij7Rc+9K4qXVvd/EfOjgqA+HVMu5gqeoX0nhbJEu0wtpMzWkYmNpT/W9Zkxhk9AfUj50LF4WyjtWWehM3pM/Nt6AM9PGgR+i94oihYHGdmMHql+LQi0T6CO+1vxK8/g== 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, Dec 03, 2025 at 09:42:59AM +0100, Michal Hocko wrote: > On Wed 03-12-25 03:35:51, Gregory Price wrote: > > if (!ret) { > > /* > > * TODO: fatal migration failures should bail > > * out > > */ > > do_migrate_range(pfn, end_pfn); > > } > > > > Maybe it's time to implement the bail out? > > That would be great but can we tell transient from permanent migration > failures? Maybe long term pins could be treated as permanent failure. > I see deep in migration code `migrate_pages_batch()` we would return "Some other failure" as fatal: switch(rc) { case -ENOMEM: ... /* Note: some long-term pin handing is done here */ break; case -EAGAIN: ... break; case 0: ... list_move_tail(&folio->lru, &unmap_folios); list_add_tail(&dst->lru, &dst_folios); break; default: /* * Permanent failure (-EBUSY, etc.): * unlike -EAGAIN case, the failed folio is * removed from migration folio list and not * retried in the next outer loop. */ nr_failed++; stats->nr_thp_failed += is_thp; stats->nr_failed_pages += nr_pages; break; } So at a minimum we could at least check for !(ENOMEM,EAGAIN) I suppose? It's unclear to me based on this code here how longerm pinning would return. Maybe David knows. ~Gregory