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a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=dt9VzEwgFbYA:10 a=GoEa3M9JfhUA:10 a=NU-prHslJhMlhDTFa5AA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTA3MDA5OCBTYWx0ZWRfX/6au1OcIBR3A 8GdVQ43lYJ9d5PynckkYCKP7rEv8qYg+476QcgyGhjI3E5QHb5ZDb1q/Og0CPBqV/JQ+PyfOqRk 9RXZ+/3Mx7J9nZlDlIT/v6n90dms9MM/iFpvJgB02F5alAT/O4d8QdVyFVVZJlb49Vu6NhY9LBJ C1KIpfp20fOuoOH5A1mFKm/93/gVQY6EDWk9oW8EBPniIHiOYirFWfy1dn7S0OUsakM/ZCU1Iu1 PGSrSiyYsN4mGAzlR+rLAE/jI/zKGSoVyMnQKUT/aYosl5539OgzEt9vxf7ihiVCaoBDyOzeR/B S3lksgUC2nmBUNgW2VRSP8A+SOTOdfMfWGmQ3aoBOUMymBH1NCmDzd4IQa5Wgqj67Oyy0aGS5Mu jV4xkI1iC4Edcy8zmyhEMtsOSH1uYLZToLTh/5VPTN64lB5lelp2lSbQhKzcOICVS0i53GpY X-Proofpoint-GUID: l8vgLcc8JsWwNfmjonnJwdO_3ky2F-af X-Proofpoint-ORIG-GUID: l8vgLcc8JsWwNfmjonnJwdO_3ky2F-af On Fri, Apr 25, 2025 at 10:27:29AM +0200, Vlastimil Babka wrote: > Since we don't control the NUMA locality of objects in percpu sheaves, > allocations with node restrictions bypass them. Allocations without > restrictions may however still expect to get local objects with high > probability, and the introduction of sheaves can decrease it due to > freed object from a remote node ending up in percpu sheaves. > > The fraction of such remote frees seems low (5% on an 8-node machine) > but it can be expected that some cache or workload specific corner cases > exist. We can either conclude that this is not a problem due to the low > fraction, or we can make remote frees bypass percpu sheaves and go > directly to their slabs. This will make the remote frees more expensive, > but if if's only a small fraction, most frees will still benefit from > the lower overhead of percpu sheaves. > > This patch thus makes remote object freeing bypass percpu sheaves, > including bulk freeing, and kfree_rcu() via the rcu_free sheaf. However > it's not intended to be 100% guarantee that percpu sheaves will only > contain local objects. The refill from slabs does not provide that > guarantee in the first place, and there might be cpu migrations > happening when we need to unlock the local_lock. Avoiding all that could > be possible but complicated so we can leave it for later investigation > whether it would be worth it. It can be expected that the more selective > freeing will itself prevent accumulation of remote objects in percpu > sheaves so any such violations would have only short-term effects. > > Another possible optimization to investigate is whether it would be > beneficial for node-restricted or strict_numa allocations to attempt to > obtain an object from percpu sheaves if the node or mempolicy (i.e. > MPOL_LOCAL) happens to want the local node of the allocating cpu. Right > now such allocations bypass sheaves, but they could probably look first > whether the first available object in percpu sheaves is local, and with > high probability succeed - and only bypass the sheaves in cases it's > not local. > > Signed-off-by: Vlastimil Babka > --- > mm/slab_common.c | 7 +++++-- > mm/slub.c | 43 +++++++++++++++++++++++++++++++++++++------ > 2 files changed, 42 insertions(+), 8 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index cc273cc45f632e16644355831132cdc391219cec..2bf83e2b85b23f4db2b311edaded4bef6b7d01de 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5924,8 +5948,15 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object, > if (unlikely(!slab_free_hook(s, object, slab_want_init_on_free(s), false))) > return; > > - if (!s->cpu_sheaves || !free_to_pcs(s, object)) > - do_slab_free(s, slab, object, object, 1, addr); > + if (s->cpu_sheaves) { > + if (likely(!IS_ENABLED(CONFIG_NUMA) || > + slab_nid(slab) == numa_node_id())) { > + free_to_pcs(s, object); Shouldn't it call do_slab_free() when free_to_pcs() failed? > + return; > + } > + } > + > + do_slab_free(s, slab, object, object, 1, addr); > } > > #ifdef CONFIG_MEMCG > > -- > 2.49.0 > > -- Cheers, Harry / Hyeonggon