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X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: wTUAK69kD85RqjiQhyqSfQ15i1HuAYLX0UTaJ1NESJq1WdKZaboIE3XmVGqDrRaA X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB9008 X-Rspamd-Queue-Id: E2DC820002 X-Rspam-User: X-Stat-Signature: ysg61nnwhahkda3g16fmgdyx87u85g3y X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1792550725-53355 X-HE-Meta: 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 uS8Bsg3L au6vlv08maD5o0zTQL4jyLQa8DIFnMSqNyaitIolDfMiHACPibCG4FkqwvnIQ1nuIcH6IT3atyQzxsYecd6/ZLzg4IU5ko3ITWPAk6Sy99bgxmwRjy2xQmwGZw/OsVAmWwUHtx4GO3tbaX7WPJDi2ktjlb0+FoQobmCYEtbyD9lxa8XffUvDL75kfQDfOE9IX7uS7qLV6ICJzwr+iWShg9aCDdw9kqYZ5qRlzRcfPbSwcEuRk2DQ8akQ+Ro7ocB2hpuqtsj5f3vTJs/odUoLJ1YgIo5xq3sHE84nw1hDiSYWQe9M+1X+DjFehoI0h1t6JRYSWg6vsNCqwzIRsjvvrMgMD32P6K6NYteZYegn2RT5GRFFUsgxGSyXHaNyhrunySU86Yz7Cnopvqqln9KnR3r7FWe3GyGtb8PhHna3JI9cqY61J2rqWI4qR4g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 19 Oct 2026, at 19:06, Joanne Koong wrote: > move_folios_to_lru(), folio_batch_move_lru() and folios_put_refs() call= > folio_unqueue_deferred_split() on folios where the refcount has dropped= > to zero. In these paths, folio_unqueue_deferred_split() is called with > the lruvec lock often held (move_folios_to_lru() always holds it and > folio_batch_move_lru()/folios_put_refs() usually hold it for every foli= o > in the batch except the first). However, it's not needed to hold the > lruvec lock. > > The lruvec lock protects folio->lru and the reclaim LRU lists whereas > the deferred split queue lives on folio->_deferred_list in > deferred_split_lru. The deferred_split_lru is a list_lru with its own > per-memcg per-node lock. > > There are already other existing callers that call > folio_unqueue_deferred_split() without holding the lruvec lock (eg > __folio_put(), shrink_folio_list(), __folio_migrate_mapping(), ...). > > Add folio_batch_unqueue_deferred_split() and use it in > move_folios_to_lru(), folio_batch_move_lru(), and folios_put_refs() to > unqueue each batch of zero-refcount folios from the deferred split list= > after the lruvec lock is released and before > mem_cgroup_uncharge_folios(). This helps shorten the lruvec lock's > critical sections, which run with IRQs disabled and are highly > contended. > > This came out of the discussion on v2 of the mTHP shrinker series [1], > where queueing small mTHP folios on the deferred split queue was found > to regress Barry's fault microbenchmark. With [1] applied and > khugepaged/max_ptes_none=3D0 so that every folio is queued, perf lock > contention showed that the extra cost came from waiting on the lruvec > lock in the free path. > > Test setup: 2-socket Intel Skylake, 40 cores / 80 threads, memory bound= > to node 0 so that all threads contend on one lruvec, with each of 80 > threads faulting in and unmapping 16 MB of anonymous memory 200 times. > With only 16K mTHP enabled, this patch reduces the queueing cost from > 15% runtime to noise, and lruvec lock wait time (summed across threads)= > drops from 491 seconds to 38 seconds. Most of the remaining contention > moves to the deferred split list_lru lock, but runtime still drops back= > to the unqueued baseline. This test uses a worst-case configuration ([1= ] > is expected to only queue folios of 2M and larger). > > [1] https://lore.kernel.org/linux-mm/CAJnrk1a2PpUGTsCgS7jct2KET4K2zAL+_= h+te8G1MaU9bXs99w@mail.gmail.com/ > > Reviewed-by: Lance Yang > Signed-off-by: Joanne Koong > --- > v2 -> v3: > - Move benchmark results into the commit message (Lance, Barry) > v2 link: https://lore.kernel.org/linux-mm/20261017004555.2890038-1-joan= nelkoong@gmail.com/ > > v1 -> v2: > - Reword comment in folio_batch_move_lru() (David) > v1 link: https://lore.kernel.org/linux-mm/20261013221307.850803-1-joann= elkoong@gmail.com/ > > mm/folio.c | 24 +++++++++++++++++++----- > mm/internal.h | 1 + > mm/vmscan.c | 3 ++- > 3 files changed, 22 insertions(+), 6 deletions(-) > LGTM. Reviewed-by: Zi Yan Best Regards, Yan, Zi