Re: [PATCH 0/1] alloc_tag: add per-numa node stats

[Kent Overstreet <kent.overstreet@linux.dev>]

On Thu, May 29, 2025 at 06:39:43PM -0600, Casey Chen wrote:
> The patch is based 4aab42ee1e4e ("mm/zblock: make active_list rcu_list")
> from branch mm-new of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> 
> The patch adds per-NUMA alloc_tag stats. Bytes/calls in total and per-NUMA
> nodes are displayed in a single row for each alloc_tag in /proc/allocinfo.
> Also percpu allocation is marked and its stats is stored on NUMA node 0.
> For example, the resulting file looks like below.
> 
> percpu y total         8588     2147 numa0         8588     2147 numa1            0        0 kernel/irq/irqdesc.c:425 func:alloc_desc
> percpu n total       447232     1747 numa0       269568     1053 numa1       177664      694 lib/maple_tree.c:165 func:mt_alloc_bulk
> percpu n total        83200      325 numa0        30976      121 numa1        52224      204 lib/maple_tree.c:160 func:mt_alloc_one
> ...
> percpu n total       364800     5700 numa0       109440     1710 numa1       255360     3990 drivers/net/ethernet/mellanox/mlx5/core/cmd.c:1410 [mlx5_core] func:mlx5_alloc_cmd_msg
> percpu n total      1249280    39040 numa0       374784    11712 numa1       874496    27328 drivers/net/ethernet/mellanox/mlx5/core/cmd.c:1376 [mlx5_core] func:alloc_cmd_box

Err, what is 'percpu y/n'?

> 
> To save memory, we dynamically allocate per-NUMA node stats counter once the
> system boots up and knows how many NUMA nodes available. percpu allocators
> are used for memory allocation hence increase PERCPU_DYNAMIC_RESERVE.
> 
> For in-kernel alloc_tags, pcpu_alloc_noprof() is called so the memory for
> these counters are not accounted in profiling stats.
> 
> For loadable modules, __alloc_percpu_gfp() is called and memory is accounted.

Intruiging, but I'd make it a kconfig option, AFAIK this would mainly be
of interest to people looking at optimizing allocations to make sure
they're on the right numa node?