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X-CSE-ConnectionGUID: hsMEt52uS56BSJW6W5b5jg== X-CSE-MsgGUID: n4nNAhhWRHSiXJaTV9VItA== X-IronPort-AV: E=McAfee;i="6800,10657,11672"; a="73495807" X-IronPort-AV: E=Sophos;i="6.21,230,1763452800"; d="scan'208";a="73495807" Received: from fmviesa007.fm.intel.com ([10.60.135.147]) by orvoesa107.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2026 00:42:04 -0800 X-CSE-ConnectionGUID: tl6lmrRvSnC54MaXItf+gA== X-CSE-MsgGUID: lxPScIAeT6ijGyndnsl7nA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,230,1763452800"; d="scan'208";a="204797888" Received: from liuzhao-optiplex-7080.sh.intel.com (HELO localhost) ([10.239.160.39]) by fmviesa007.fm.intel.com with ESMTP; 16 Jan 2026 00:42:00 -0800 Date: Fri, 16 Jan 2026 17:07:30 +0800 From: Zhao Liu To: Vlastimil Babka Cc: Hao Li , akpm@linux-foundation.org, harry.yoo@oracle.com, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, tim.c.chen@intel.com, yu.c.chen@intel.com, zhao1.liu@intel.com Subject: Re: [PATCH v2] slub: keep empty main sheaf as spare in __pcs_replace_empty_main() Message-ID: References: <20251210002629.34448-1-haoli.tcs@gmail.com> <6be60100-e94c-4c06-9542-29ac8bf8f013@suse.cz> 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 Content-Disposition: inline In-Reply-To: <6be60100-e94c-4c06-9542-29ac8bf8f013@suse.cz> > > The following is the perf data comparing 2 tests w/o fix & with this fix: > > > > # Baseline Delta Abs Shared Object Symbol > > # ........ ......... ....................... .................................... > > # > > 61.76% +4.78% [kernel.vmlinux] [k] native_queued_spin_lock_slowpath > > 0.93% -0.32% [kernel.vmlinux] [k] __slab_free > > 0.39% -0.31% [kernel.vmlinux] [k] barn_get_empty_sheaf > > 1.35% -0.30% [kernel.vmlinux] [k] mas_leaf_max_gap > > 3.22% -0.30% [kernel.vmlinux] [k] __kmem_cache_alloc_bulk > > 1.73% -0.20% [kernel.vmlinux] [k] __cond_resched > > 0.52% -0.19% [kernel.vmlinux] [k] _raw_spin_lock_irqsave > > 0.92% +0.18% [kernel.vmlinux] [k] _raw_spin_lock > > 1.91% -0.15% [kernel.vmlinux] [k] zap_pmd_range.isra.0 > > 1.37% -0.13% [kernel.vmlinux] [k] mas_wr_node_store > > 1.29% -0.12% [kernel.vmlinux] [k] free_pud_range > > 0.92% -0.11% [kernel.vmlinux] [k] __mmap_region > > 0.12% -0.11% [kernel.vmlinux] [k] barn_put_empty_sheaf > > 0.20% -0.09% [kernel.vmlinux] [k] barn_replace_empty_sheaf > > 0.31% +0.09% [kernel.vmlinux] [k] get_partial_node > > 0.29% -0.07% [kernel.vmlinux] [k] __rcu_free_sheaf_prepare > > 0.12% -0.07% [kernel.vmlinux] [k] intel_idle_xstate > > 0.21% -0.07% [kernel.vmlinux] [k] __kfree_rcu_sheaf > > 0.26% -0.07% [kernel.vmlinux] [k] down_write > > 0.53% -0.06% libc.so.6 [.] __mmap > > 0.66% -0.06% [kernel.vmlinux] [k] mas_walk > > 0.48% -0.06% [kernel.vmlinux] [k] mas_prev_slot > > 0.45% -0.06% [kernel.vmlinux] [k] mas_find > > 0.38% -0.06% [kernel.vmlinux] [k] mas_wr_store_type > > 0.23% -0.06% [kernel.vmlinux] [k] do_vmi_align_munmap > > 0.21% -0.05% [kernel.vmlinux] [k] perf_event_mmap_event > > 0.32% -0.05% [kernel.vmlinux] [k] entry_SYSRETQ_unsafe_stack > > 0.19% -0.05% [kernel.vmlinux] [k] downgrade_write > > 0.59% -0.05% [kernel.vmlinux] [k] mas_next_slot > > 0.31% -0.05% [kernel.vmlinux] [k] __mmap_new_vma > > 0.44% -0.05% [kernel.vmlinux] [k] kmem_cache_alloc_noprof > > 0.28% -0.05% [kernel.vmlinux] [k] __vma_enter_locked > > 0.41% -0.05% [kernel.vmlinux] [k] memcpy > > 0.48% -0.04% [kernel.vmlinux] [k] mas_store_gfp > > 0.14% +0.04% [kernel.vmlinux] [k] __put_partials > > 0.19% -0.04% [kernel.vmlinux] [k] mas_empty_area_rev > > 0.30% -0.04% [kernel.vmlinux] [k] do_syscall_64 > > 0.25% -0.04% [kernel.vmlinux] [k] mas_preallocate > > 0.15% -0.04% [kernel.vmlinux] [k] rcu_free_sheaf > > 0.22% -0.04% [kernel.vmlinux] [k] entry_SYSCALL_64 > > 0.49% -0.04% libc.so.6 [.] __munmap > > 0.91% -0.04% [kernel.vmlinux] [k] rcu_all_qs > > 0.21% -0.04% [kernel.vmlinux] [k] __vm_munmap > > 0.24% -0.04% [kernel.vmlinux] [k] mas_store_prealloc > > 0.19% -0.04% [kernel.vmlinux] [k] __kmalloc_cache_noprof > > 0.34% -0.04% [kernel.vmlinux] [k] build_detached_freelist > > 0.19% -0.03% [kernel.vmlinux] [k] vms_complete_munmap_vmas > > 0.36% -0.03% [kernel.vmlinux] [k] mas_rev_awalk > > 0.05% -0.03% [kernel.vmlinux] [k] shuffle_freelist > > 0.19% -0.03% [kernel.vmlinux] [k] down_write_killable > > 0.19% -0.03% [kernel.vmlinux] [k] kmem_cache_free > > 0.27% -0.03% [kernel.vmlinux] [k] up_write > > 0.13% -0.03% [kernel.vmlinux] [k] vm_area_alloc > > 0.18% -0.03% [kernel.vmlinux] [k] arch_get_unmapped_area_topdown > > 0.08% -0.03% [kernel.vmlinux] [k] userfaultfd_unmap_complete > > 0.10% -0.03% [kernel.vmlinux] [k] tlb_gather_mmu > > 0.30% -0.02% [kernel.vmlinux] [k] ___slab_alloc > > > > I think the insteresting item is "get_partial_node". It seems this fix > > makes "get_partial_node" slightly more frequent. HMM, however, I still > > can't figure out why this is happening. Do you have any thoughts on it? > > I'm not sure if it's statistically significant or just noise, +0.09% could > be noise? small number does't always mean it's noise. When perf samples get_partial_node on the spin lock call chain, its subroutines (spin lock) are hotter, so the proportion of subroutine execution is higher. If the function - get_partial_node itself (excluding subroutines) executes very quickly, the proportion is lower. I also expend the perf data with call chain: * w/o fix: We can calculate the proportion of spin locks introduced by get_partial_node is: 31.05% / 49.91% = 62.21% 49.91% mmap2_processes [kernel.vmlinux] [k] native_queued_spin_lock_slowpath | --49.91%--native_queued_spin_lock_slowpath | --49.91%--_raw_spin_lock_irqsave | |--31.05%--get_partial_node | | | |--23.66%--get_any_partial | | ___slab_alloc | | | --7.40%--___slab_alloc | __kmem_cache_alloc_bulk | |--10.84%--barn_get_empty_sheaf | | | |--6.18%--__kfree_rcu_sheaf | | kvfree_call_rcu | | | --4.66%--__pcs_replace_empty_main | kmem_cache_alloc_noprof | |--5.10%--barn_put_empty_sheaf | | | --5.09%--__pcs_replace_empty_main | kmem_cache_alloc_noprof | |--2.01%--barn_replace_empty_sheaf | __pcs_replace_empty_main | kmem_cache_alloc_noprof | --0.78%--__put_partials | --0.78%--__kmem_cache_free_bulk.part.0 rcu_free_sheaf * with fix: Similarly, the proportion of spin locks introduced by get_partial_node is: 39.91% / 42.82% = 93.20% 42.82% mmap2_processes [kernel.vmlinux] [k] native_queued_spin_lock_slowpath | ---native_queued_spin_lock_slowpath | --42.82%--_raw_spin_lock_irqsave | |--39.91%--get_partial_node | | | |--28.25%--get_any_partial | | ___slab_alloc | | | --11.66%--___slab_alloc | __kmem_cache_alloc_bulk | |--1.09%--barn_get_empty_sheaf | | | --0.90%--__kfree_rcu_sheaf | kvfree_call_rcu | |--0.96%--barn_replace_empty_sheaf | __pcs_replace_empty_main | kmem_cache_alloc_noprof | --0.77%--__put_partials __kmem_cache_free_bulk.part.0 rcu_free_sheaf So, 62.21% -> 93.20% could reflect that get_partial_node contribute more overhead at this point. > > So, I'd like to know if you think dynamically or adaptively adjusting > > capacity is a worthwhile idea. > > In the followup series, there will be automatically determined capacity to > roughly match the current capacity of cpu partial slabs: > > https://lore.kernel.org/all/20260112-sheaves-for-all-v2-4-98225cfb50cf@suse.cz/ > > We can use that as starting point for further tuning. But I suspect making > it adjust dynamically would be complicated. Thanks, will continue to evaluate this series. Regards, Zhao