Re: [PATCH v3] x86/mce: Dynamically size space for machine check records

[Naik, Avadhut]

On 3/7/2024 13:27, Tony Luck wrote:
> Systems with a large number of CPUs may generate a large
> number of machine check records when things go seriously
> wrong. But Linux has a fixed buffer that can only capture
> a few dozen errors.
> 
> Allocate space based on the number of CPUs (with a minimum
> value based on the historical fixed buffer that could store
> 80 records).
> 
> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> Reviewed-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
> ---
> 
> Changes since V2; Link: https://lore.kernel.org/all/20240307000256.34352-1-tony.luck@xxxxxxxxx/
> 
> Boris: Eliminate "out:" label in mce_gen_pool_create()
> 
> Sohil: Added Reviewed-by tag
> 
>  arch/x86/kernel/cpu/mce/genpool.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/genpool.c b/arch/x86/kernel/cpu/mce/genpool.c
> index fbe8b61c3413..cadf28662a70 100644
> --- a/arch/x86/kernel/cpu/mce/genpool.c
> +++ b/arch/x86/kernel/cpu/mce/genpool.c
> @@ -16,14 +16,14 @@
>   * used to save error information organized in a lock-less list.
>   *
>   * This memory pool is only to be used to save MCE records in MCE context.
> - * MCE events are rare, so a fixed size memory pool should be enough. Use
> - * 2 pages to save MCE events for now (~80 MCE records at most).
> + * MCE events are rare, so a fixed size memory pool should be enough.
> + * Allocate on a sliding scale based on number of CPUs.
>   */
> -#define MCE_POOLSZ	(2 * PAGE_SIZE)
> +#define MCE_MIN_ENTRIES	80
> +#define MCE_PER_CPU	2
>  
>  static struct gen_pool *mce_evt_pool;
>  static LLIST_HEAD(mce_event_llist);
> -static char gen_pool_buf[MCE_POOLSZ];
>  
>  /*
>   * Compare the record "t" with each of the records on list "l" to see if
> @@ -118,22 +118,32 @@ int mce_gen_pool_add(struct mce *mce)
>  
>  static int mce_gen_pool_create(void)
>  {
> +	int mce_numrecords, mce_poolsz, order;
>  	struct gen_pool *tmpp;
>  	int ret = -ENOMEM;
> +	void *mce_pool;
>  
> -	tmpp = gen_pool_create(ilog2(sizeof(struct mce_evt_llist)), -1);
> +	order = order_base_2(sizeof(struct mce_evt_llist));
> +	tmpp = gen_pool_create(order, -1);
>  	if (!tmpp)
> -		goto out;
> +		return ret;
>  
> -	ret = gen_pool_add(tmpp, (unsigned long)gen_pool_buf, MCE_POOLSZ, -1);
> +	mce_numrecords = max(MCE_MIN_ENTRIES, num_possible_cpus() * MCE_PER_CPU);
> +	mce_poolsz = mce_numrecords * (1 << order);
> +	mce_pool = kmalloc(mce_poolsz, GFP_KERNEL);
> +	if (!mce_pool) {
> +		gen_pool_destroy(tmpp);
> +		return ret;
> +	}
> +	ret = gen_pool_add(tmpp, (unsigned long)mce_pool, mce_poolsz, -1);
>  	if (ret) {
>  		gen_pool_destroy(tmpp);
> -		goto out;
> +		kfree(mce_pool);
> +		return ret;
>  	}
>  
>  	mce_evt_pool = tmpp;
>  
> -out:
>  	return ret;
>  }
>  
> 
> base-commit: d206a76d7d2726f3b096037f2079ce0bd3ba329b

LGTM!

Reviewed-by: Avadhut Naik <avadhut.naik@xxxxxxx>

-- 
Thanks,
Avadhut Naik