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b=BKs6zCBdwGPsyEPwcs1gEVvu5t2PJcOt+xtaio0LA4TKyf8lLFrd2/NiWZlIoXfOi 3z+wsZxhQX0ztsosa+/WOSjyaKs8E9Q7eMBuK6cGFfRKgif8lnujjVbS21YtkK27bx Ge7tHzYiOEvrSFfu48MX8F541K4kGRgOh61/5PQlNcXKFY0mB3Gx9J7ph9R9g//nye i0z4JnvRfZkB2YlYbEogk98y1YZUPv6M19fO9V4mGvmfHZO+zUFWQFeNrzgvK0azlB fS19ls5f6wv6z04NQbn6QxcuEHEF8k+c0nUpfFCMe9oec1UcBqRNHqeG5Utz6u81Q0 ieU48pd8ECimQ== Message-ID: <8b89bb59-6b6a-4a79-a571-e97b9ae5287f@kernel.org> Date: Wed, 3 Dec 2025 10:15:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free To: Gregory Price , 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 References: <20251201060009.1420792-1-aboorvad@linux.ibm.com> <20251201094112.07eb1e588b6da2ee70c4641d@linux-foundation.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: A0F881C000D X-Rspamd-Server: rspam11 X-Stat-Signature: fpbnr77f16dtd7a9z3h7eiq9p5tdnzd3 X-HE-Tag: 1764753312-504142 X-HE-Meta: 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 4hL1EBlC 9sS/QsoogFFXphrDc/SM6XhUtnXEz/+DyuHWhk0/VQtEuzdiPKZd29FrrNJR2I50piCEvXiaVfqVP8x5yr3q0a1g/BQEwBXb0ttZefZ+DDFb2hwztO7SFo0xROUxPFd4bpeHZ2F5xvEahFxGugIybVTTAzK/kiMUkqO6fWcInVCkh6rd8x0uGPoHR9GI+37c/JEv1H7IOewjXUPaKFzMvKjKEg/82ilaS8qefOAwNrlo9haImPkyFXmfpl7NmHELI9G6A4WC3FrlCxBqCEFgNnhMLkZX9qEwoJsBbgJj/lsRW8ATXTX+FPfkLpg== 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 12/3/25 09:59, Gregory Price wrote: > 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. I would assume that additional references will always result in -EAGAIN. Remember that we cannot distinguish short-term pins from long-term pins. We should never have longterm-pins on ZONE_MOVABLE, unless something broke that contract and needs to be fixed. -- Cheers David