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 kPVfYGsD 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Feb 25, 2026 at 01:32:36PM +0800, Hao Li wrote: > On Tue, Feb 24, 2026 at 05:07:18PM +0800, Ming Lei wrote: > > Hi Harry, > > > > On Tue, Feb 24, 2026 at 02:00:15PM +0900, Harry Yoo wrote: > > > On Tue, Feb 24, 2026 at 10:52:28AM +0800, Ming Lei wrote: > > > > Hello Vlastimil and MM guys, > > > > > > Hi Ming, thanks for the report! > > > > > > > The SLUB "sheaves" series merged via 815c8e35511d ("Merge branch > > > > 'slab/for-7.0/sheaves' into slab/for-next") introduces a severe > > > > performance regression for workloads with persistent cross-CPU > > > > alloc/free patterns. ublk null target benchmark IOPS drops > > > > significantly compared to v6.19: from ~36M IOPS to ~13M IOPS (~64% > > > > drop). > > > > > > > > Bisecting within the sheaves series is blocked by a kernel panic at > > > > 17c38c88294d ("slab: remove cpu (partial) slabs usage from allocation > > > > paths"), so the exact first bad commit could not be identified. > > > > > > Ouch. Why did it crash? > > > > [ 16.162422] Oops: general protection fault, probably for non-canonical address 0xdead000000000110: 0000 [#1] SMP NOPTI > > [ 16.162426] CPU: 44 UID: 0 PID: 908 Comm: (udev-worker) Not tainted 6.19.0-rc5_master+ #116 PREEMPT(lazy) > > [ 16.162429] Hardware name: Giga Computing MZ73-LM2-000/MZ73-LM2-000, BIOS R19_F40 05/12/2025 > > [ 16.162430] RIP: 0010:__put_partials+0x2f/0x140 > > [ 16.162437] Code: 41 57 41 56 49 89 f6 41 55 49 89 fd 31 ff 41 54 45 31 e4 55 53 48 83 ec 18 48 c7 44 24 10 00 00 00 00 eb 03 48 89 df 4c9 > > [ 16.162438] RSP: 0018:ff5117c0ca2dfa60 EFLAGS: 00010086 > > [ 16.162441] RAX: 0000000000000001 RBX: ff1b266981200d80 RCX: 0000000000000246 > > [ 16.162442] RDX: ff1b266981200d90 RSI: ff1b266981200d90 RDI: ff1b266981200d80 > > [ 16.162442] RBP: dead000000000100 R08: 0000000000000000 R09: ffffffffa761bf5e > > [ 16.162443] R10: ffb6d4b7841d5400 R11: ff1b2669800575c0 R12: 0000000000000000 > > [ 16.162444] R13: ff1b2669800575c0 R14: dead000000000100 R15: ffb6d4b7846be410 > > [ 16.162445] FS: 00007f5fdccc23c0(0000) GS:ff1b267902427000(0000) knlGS:0000000000000000 > > [ 16.162446] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [ 16.162446] CR2: 0000559824c6c058 CR3: 000000011fb49001 CR4: 0000000000f71ef0 > > [ 16.162447] PKRU: 55555554 > > [ 16.162448] Call Trace: > > [ 16.162450] > > [ 16.162452] kmem_cache_free+0x410/0x490 > > [ 16.162454] do_readlinkat+0x14e/0x180 > > [ 16.162459] __x64_sys_readlinkat+0x1c/0x30 > > [ 16.162461] do_syscall_64+0x7e/0x6b0 > > [ 16.162465] ? post_alloc_hook+0xb9/0x140 > > [ 16.162468] ? get_page_from_freelist+0x478/0x720 > > [ 16.162470] ? path_openat+0xb3/0x2a0 > > [ 16.162472] ? __alloc_frozen_pages_noprof+0x192/0x350 > > [ 16.162474] ? count_memcg_events+0xd6/0x210 > > [ 16.162476] ? memcg1_commit_charge+0x7a/0xa0 > > [ 16.162479] ? mod_memcg_lruvec_state+0xe7/0x2d0 > > [ 16.162481] ? charge_memcg+0x48/0x80 > > [ 16.162482] ? lruvec_stat_mod_folio+0x85/0xd0 > > [ 16.162484] ? __folio_mod_stat+0x2d/0x90 > > [ 16.162487] ? set_ptes.isra.0+0x36/0x80 > > [ 16.162490] ? do_anonymous_page+0x100/0x4a0 > > [ 16.162492] ? __handle_mm_fault+0x45d/0x6f0 > > [ 16.162493] ? count_memcg_events+0xd6/0x210 > > [ 16.162494] ? handle_mm_fault+0x212/0x340 > > [ 16.162495] ? do_user_addr_fault+0x2b4/0x7b0 > > [ 16.162500] ? irqentry_exit+0x6d/0x540 > > [ 16.162502] ? exc_page_fault+0x7e/0x1a0 > > [ 16.162503] entry_SYSCALL_64_after_hwframe+0x76/0x7e > > For this problem, I have a hypothesis which is inspired by a comment in the > patch "slab: remove cpu (partial) slabs usage from allocation paths": > > /* > * get a single object from the slab. This might race against __slab_free(), > * which however has to take the list_lock if it's about to make the slab fully > * free. > */ > > My understanding is that this comment is pointing out a possible race between > __slab_free() and get_from_partial_node(). Since __slab_free() takes > n->list_lock when it is about to make the slab fully free, and > get_from_partial_node() also takes the same lock, the two paths should be > mutually excluded by the lock and thus safe. > > However, I'm wondering if there could be another race window. Suppose CPU0's > get_from_partial_node() has already finished __slab_update_freelist(), but has > not yet reached remove_partial(). In that gap, another CPU1 could free an object > to the same slab via __slab_free(). CPU1 would observe was_full == 1 (due to the > previous get_from_partial_node()->__slab_update_freelist() on CPU0), and then > > __slab_free() will call put_cpu_partial(s, slab, 1) without holding > n->list_lock, trying to add this slab to the CPU partial list. If CPU1 observes was_full == 1, it should spin on n->list_lock and wait for CPU0 to release the lock. And CPU0 will remove the slab from the partial list before releasing the lock. Or am I missing something? > In that case, > both paths would operate on the same union field in struct slab, which might > lead to list corruption. Not sure how the scenario you describe could happen: CPU 0 CPU1 - get_from_partial_node() -> spin_lock(&n->list_lock) - __slab_free() -> __slab_update_freelist(), slab becomes full -> was_full == 1 -> spin_lock(&n->list_lock) // starts spining -> if (!new.freelist) -> remove_partial() -> spin_unlock() -> spin_lock(&n->list_lock) // acquired! -> slab_update_freelist() -> spin_unlock(&n->list_lock) -- Cheers, Harry / Hyeonggon