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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-87149316347sm108893927b3.15.2026.09.09.02.39.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Sep 2026 02:39:25 -0700 (PDT) Date: Wed, 9 Sep 2026 02:39:08 -0700 (PDT) From: Hugh Dickins To: Andrew Morton cc: Ackerley Tng , Alexander Viro , Alexandre Ghiti , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , Claudio Imbrenda , David Hildenbrand , Hugh Dickins , JP Kobryn , Jan Kara , Jens Axboe , Johannes Weiner , Kairui Song , Kiryl Shutsemau , Lance Yang , Leonardo Bras , Lorenzo Stoakes , Marcelo Tosatti , Matthew Wilcox , Mel Gorman , Miaohe Lin , Michal Hocko , Minchan Kim , Muchun Song , Oscar Salvador , Peter Zijlstra , Qi Zheng , Rik van Riel , Sebastian Andrzej Siewior , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka , Yang Shi , Yu Zhao , Zach O'Keefe , Zi Yan , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2 00/26] mm/fbatch: drain lru_add_drain() and _all() Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII [PATCH v2 00/26] mm/fbatch: drain lru_add_drain() and _all() This series was prompted by lru_add_drain_all() appearing in watchdog backtraces: not to blame, but blocked on an unresponsive CPU to run its workqueue. lru_add_drain_all() is a heavyweight operation, which we often hope to avoid by a much lighter lru_add_drain(); but even those local drains can aggravate the lruvec lock contention which per-cpu fbatches are intended to ease. Now let the folios on the lru_add and other per-cpu fbatches remain there, isolatable, with PG_lru set and refcount unraised, just like when on an actual LRU. Then many calls to lru_add_drain() and _all() can be removed. It's something I've wanted to do for years, tried several times, but only hit on a good way to do it a few weeks ago: now it's uncomfortable to watch others wrestling with the drainage, while I'm sitting on this. The key idea came from the "if (!folio_test_clear_lru(folio)) continue;". If we don't mind missing to take an action on rare occasions, then maybe we won't mind taking an action on the wrong folio on rare occasions, so long as it is a folio consenting to PG_lru rules. No new locking, but relies on folio_try_get() and folio_test_clear_lru() even on the lru_add fbatch; with use of bits not set in aligned pointers, and some try_cmpxchg()ing. Speculative references to folios are already accepted: this adds another source of them. Performance? You (and the bots) tell me. I'm considering this as a cleanup, to make life easier for developers. I expect that some loads will show improvement, but also expect some disappointments (perhaps I go too far against lru_cache_disable()? or not far enough). The timing is not good: I'm taking three weeks off today; but it's best to get this out in the open early. If it's welcome in principle for 7.4, but changes needed, maybe someone else can step up to shepherd it through; otherwise, I can take it up again for 7.5. Rebased and retested on Linus's v7.3-rc2 tree, after adding two mm.git dependencies which did not get into rc2, but can be expected in rc3: Shakeel's "mm/mlock: use the IRQ-safe accessor for NR_MLOCK in __munlock_folio()" and Ackerley's "mm/folio: EXPORT_SYMBOL_FOR_KVM( lru_cache_drain_for_folio)". Those two are now in mm-hotfixes-stable (e14a34548064 and 7891fbb9512f respectively: thanks to Andrew) as of mm-everything-2026-09-09-06-32, and the series applied and briefly tested over 09-09's earlier mm-everything, so I'm giving a hopeful but not entirely honest base-commit below. v1 posted on 24 August had 25 patches, with 26/25 added later: Link: https://lore.kernel.org/linux-mm/14a16945-529b-8bc0-ab38-3ea97e54e223@google.com/ 01/26 mm/fbatch: remove !CONFIG_SMP special case of folio_activate() v2: added Ack from David, R-b Vlastimil 02/26 mm/fbatch: allow folios_put_refs() to skip xa_is_value() entries v2: added Ack from David, R-b Vlastimil 03/26 mm/fbatch: temporarily disable lazyfree and mlock+munlock batching v2: added R-b Vlastimil 04/26 mm/fbatch: lru bit set, no extra ref, while folio on per-cpu fbatch v2: added comment on Bit 1 of page->lru.next per Kiryl and Matthew READ/WRITE_ONCE smp_mb__before_atomic per 07/25 discussion with Kiryl fixed (commented out) BUG_ON in lru_add_del_folio() 05/26 mm/fbatch: lru_add_del_folio()+folio_add_lru() after clear_lru() 06/26 mm/fbatch: fbatch_drain_lazyfree(onstack fbatch) before ptl unlock 07/26 mm/fbatch: LRU_NEXT_ACTIVATE bit to optimize folio_activate() v2: hunk in lru_add_del_folio() updated according to mods in 04/26 08/26 mm/fbatch: replace mlock_new_folio() by __folio_add_lru(,mlockit) v2: updated 04/26 Bit 1 comment on folio_add_lru() to __folio_add_lru() 09/26 mm/fbatch: restore mlock+munlock batching, without extra ref v2: rediffed around Shakeel's NR_MLOCK fix, fixed unknowingly in v1 10/26 mm/fbatch: remove several uses of mlock_drain_local() 11/26 mm/fbatch: remove migration's PAGE_WAS_MLOCKED lru_add_drain() v2: conversely, use !folio_evictable() in isolate_migratepages_block() 12/26 mm/fbatch: remove percpu_pvec_drained and folios_put() 13/26 mm/fbatch: no lru_add drain to collect_longterm_unpinnable_folios() v2: revert David's rc1 lru_cache_drain_for_folio() from mm/folio.c, and Ackerley's EXPORT for KVM; but keep an inline stub in swap.h 14/26 mm/fbatch: no lru_add_drain() nor _all() for memfd_wait_for_pins() 15/26 mm/fbatch: remove shake_folio() shake_page() from memory-failure v2: added Ack from Miaohe 16/26 mm/fbatch: remove lru_cache_disable() from NUMA folio migration 17/26 mm/fbatch: no lru_cache_disable() in __alloc_contig_migrate_range() 18/26 mm/fbatch: remove lru_add_drain() and _all() calls from various 19/26 mm/fbatch: vm/stat_refresh include lru_add_drain() on each cpu 20/26 s390/fbatch: no lru_add_drain_all() in s390_wiggle_split_folio() 21/26 block/fbatch: no lru_add_drain_all() in invalidate_bdev() 22/26 fs/fbatch: drop_caches invalidate_bh_lrus() not lru_add_drain_all() 23/26 fs,mm/fbatch: use invalidate_bh_lrus() not invalidate_bh_lrus_cpu() 24/26 fs,mm/fbatch: lru_cache_disable() keep off buffer_head lrus only 25/26 mm/fbatch: move lru_add_drain_all() declaration to mm/internal.h 26/26 mm/fbatch: drop reference inside the loop when draining Documentation/mm/unevictable-lru.rst | 2 +- arch/s390/kernel/uv.c | 1 - block/bdev.c | 1 - fs/buffer.c | 40 +-- fs/drop_caches.c | 4 +- include/linux/buffer_head.h | 8 +- include/linux/folio_batch.h | 7 +- include/linux/huge_mm.h | 6 +- include/linux/mm.h | 18 -- include/linux/mm_inline.h | 29 ++ include/linux/mm_types.h | 14 +- include/linux/swap.h | 23 +- mm/compaction.c | 27 +- mm/fadvise.c | 17 +- mm/folio.c | 436 +++++++++------------------ mm/gup.c | 9 - mm/huge_memory.c | 16 +- mm/hwpoison-inject.c | 1 - mm/internal.h | 15 +- mm/khugepaged.c | 11 - mm/ksm.c | 12 - mm/madvise.c | 9 +- mm/memfd.c | 6 +- mm/memory-failure.c | 38 +-- mm/memory.c | 14 +- mm/memory_hotplug.c | 4 + mm/mempolicy.c | 7 - mm/migrate.c | 13 +- mm/migrate_device.c | 9 - mm/mlock.c | 211 +++++++------ mm/page_alloc.c | 3 - mm/rmap.c | 4 - mm/shmem.c | 2 - mm/truncate.c | 17 +- mm/vmscan.c | 16 +- mm/vmstat.c | 1 + 36 files changed, 388 insertions(+), 663 deletions(-) base-commit: 7891fbb9512f127826e1d5dbf380ee212bd15eb0 Hugh