Re: [PATCH 0/3] slab: support memoryless nodes with sheaves

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

On 3/11/26 10:49, Ming Lei wrote:
> On Wed, Mar 11, 2026 at 09:25:54AM +0100, Vlastimil Babka (SUSE) wrote:
>> This is the draft patch from [1] turned into a proper series with
>> incremental changes. It's based on v7.0-rc3. It's too intrusive for a
>> 7.0 hotfix, so we'll only be able to fix/reduce the regression in 7.1. I
>> hope it's acceptable given it's a non-standard configuration, 7.0 is not
>> a LTS, and it's a perf regression, not functionality.
>> 
>> Ming can you please retest this on top of v7.0-rc3, which already has
>> fb1091febd66 ("mm/slab: allow sheaf refill if blocking is not
>> allowed"). Separate data point for v7.0-rc3 could be also useful.
>> 
>> [1] https://lore.kernel.org/all/c6a01f7e-c6eb-454b-9b9e-734526dd659d@kernel.org/
>> 
>> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
>> ---
>> Vlastimil Babka (SUSE) (3):
>>       slab: decouple pointer to barn from kmem_cache_node
>>       slab: create barns for online memoryless nodes
>>       slab: free remote objects to sheaves on memoryless nodes
> 
> Hi Vlastimil and Guys,
> 
> I re-run the test case used in https://lore.kernel.org/all/aZ0SbIqaIkwoW2mB@fedora/
> 
> - v6.19-rc5: 34M
> 
> - 815c8e35511d Merge branch 'slab/for-7.0/sheaves' into slab/for-next: 13M
> 
> - v7.0-rc3: 13M

Thanks, that's in line with your previous testing of "mm/slab: allow sheaf
refill if blocking is not allowed" making no difference here. At least we
just learned it helps other benchmarks :)

> - v7.0-rc3 + the three patches: 24M

OK. So now it might be really the total per-cpu caching capacity difference.

> # Test Machines
> 
> - AMD Zen4, dual sockets, 64 cores, 8 NUMA node(configure BIOS to use per-CCD numa, just 2 memory node)
> 
> - numactl -H:
> 
> https://lore.kernel.org/all/aZ7p9uF8H8u6RxrK@fedora/
> 
> # slab stat log
> 
> root@tomsrv:~/temp/mm/7.0-rc3/patched# (cd /sys/kernel/slab/bio-256/ && find . -type f -exec grep -aH . {} \;)
> ./remote_node_defrag_ratio:100
> ./total_objects:7344 N1=3417 N5=3927
> ./alloc_fastpath:476106437 C0=128 C1=26852005 C2=128 C3=27291181 C4=65 C5=35617011 C6=97 C7=34258221 C8=96 C9=28158690 C11=26433128 C12=128 C13=31715794 C15=28819773 C16=97 C17=26168947 C19=30768051 C20=128 C21=32964376 C23=34696825 C25=26471644 C26=130 C27=27844688 C28=97 C29=28480054 C31=29564950 C40=1 C42=2 C63=2
> ./cpu_slabs:0
> ./objects:7265 N1=3374 N5=3891
> ./sheaf_return_slow:0
> ./objects_partial:533 N1=212 N5=321
> ./sheaf_return_fast:0
> ./cpu_partial:0
> ./free_slowpath:295 C4=158 C6=136 C20=1
> ./barn_get_fail:270 C0=5 C1=16 C2=5 C3=6 C4=3 C5=21 C6=4 C7=14 C8=2 C9=7 C11=23 C12=3 C13=10 C15=19 C16=3 C17=4 C19=25 C20=5 C21=22 C23=6 C25=21 C26=5 C27=6 C28=1 C29=4 C31=27 C40=1 C42=1 C63=1
> ./sheaf_prefill_oversize:0
> ./skip_kfence:0
> ./min_partial:5
> ./order_fallback:0
> ./sheaf_capacity:28
> ./sheaf_flush:0
> ./free_rcu_sheaf:0
> ./sheaf_alloc:179 C0=9 C1=1 C2=4 C4=8 C5=1 C6=4 C7=65 C8=3 C10=10 C11=1 C12=2 C14=11 C15=1 C16=5 C18=8 C19=1 C20=8 C21=1 C22=5 C24=8 C25=1 C26=5 C28=5 C30=8 C31=1 C40=1 C42=1 C63=1
> ./sheaf_free:0
> ./sheaf_prefill_slow:0
> ./sheaf_prefill_fast:0
> ./poison:0
> ./red_zone:0
> ./free_slab:0
> ./slabs:144 N1=67 N5=77
> ./barn_get:17003547 C1=958985 C3=974680 C5=1272016 C7=1223494 C8=2 C9=1005661 C11=944018 C12=2 C13=1132697 C15=1029259 C16=1 C17=934602 C19=1098834 C21=1177278 C23=1239167 C25=945395 C27=994448 C28=3 C29=1017141 C31=1055864
> ./alloc_slowpath:0
> ./destroy_by_rcu:1
> ./free_rcu_sheaf_fail:0
> ./barn_put:17003623 C0=958995 C2=974679 C4=1272023 C6=1223496 C8=1005661 C10=944030 C12=1132701 C14=1029267 C16=934598 C18=1098848 C20=1177293 C22=1239162 C24=945405 C26=994447 C28=1017138 C30=1055880
> ./usersize:0
> ./sanity_checks:0
> ./barn_put_fail:0
> ./align:64
> ./alloc_node_mismatch:0
> ./alloc_slab:144 C0=2 C1=8 C2=3 C3=2 C4=1 C5=5 C6=1 C7=3 C8=2 C9=4 C11=14 C12=2 C13=7 C15=11 C16=2 C17=3 C19=20 C20=1 C21=5 C23=1 C25=13 C26=4 C27=5 C29=1 C31=21 C40=1 C42=1 C63=1
> ./free_remove_partial:0
> ./aliases:0
> ./store_user:0
> ./trace:0
> ./reclaim_account:0
> ./order:2
> ./sheaf_refill:7560 C0=140 C1=448 C2=140 C3=168 C4=84 C5=588 C6=112 C7=392 C8=56 C9=196 C11=644 C12=84 C13=280 C15=532 C16=84 C17=112 C19=700 C20=140 C21=616 C23=168 C25=588 C26=140 C27=168 C28=28 C29=112 C31=756 C40=28 C42=28 C63=28
> ./object_size:256
> ./free_fastpath:476102026 C0=26851883 C2=27291053 C4=35616664 C6=34257923 C8=28158529 C9=1 C10=26432875 C11=2 C12=31715665 C14=28819520 C16=26168783 C18=30767788 C20=32964224 C21=2 C22=34696578 C24=26471388 C26=27844558 C27=2 C28=28479894 C30=29564692 C31=2
> ./hwcache_align:1
> ./cmpxchg_double_fail:0
> ./objs_per_slab:51
> ./partial:12 N1=5 N5=7
> ./slabs_cpu_partial:0(0)
> ./free_add_partial:143 C0=3 C1=8 C2=2 C3=4 C4=11 C5=16 C6=13 C7=9 C9=3 C11=8 C12=1 C13=3 C15=8 C16=1 C17=1 C19=5 C20=5 C21=17 C23=5 C25=8 C26=1 C27=1 C28=1 C29=3 C31=6
> ./slab_size:320
> ./cache_dma:0
> 
> 
> Thanks,
> Ming
>