linux-kernel - Re: [PATCH] x86/mce: Dynamically size space for machine check records

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Message-ID: <015bf75e-bbe7-44ea-a176-9f1257f56b81@intel.com>
Date: Wed, 28 Feb 2024 17:56:26 -0800
From: Sohil Mehta <sohil.mehta@...el.com>
To: Tony Luck <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>
CC: "Naik, Avadhut" <avadnaik@....com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yazen.ghannam@....com" <yazen.ghannam@....com>, Avadhut Naik
	<avadhut.naik@....com>
Subject: Re: [PATCH] x86/mce: Dynamically size space for machine check records

A few other nits.

On 2/28/2024 3:14 PM, Tony Luck wrote:
> diff --git a/arch/x86/kernel/cpu/mce/genpool.c b/arch/x86/kernel/cpu/mce/genpool.c
> index fbe8b61c3413..a1f0a8f29cf5 100644
> --- a/arch/x86/kernel/cpu/mce/genpool.c
> +++ b/arch/x86/kernel/cpu/mce/genpool.c
> @@ -16,14 +16,13 @@
>   * 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
>  
>  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
> @@ -118,14 +117,25 @@ int mce_gen_pool_add(struct mce *mce)
>  
>  static int mce_gen_pool_create(void)
>  {
> +	int mce_numrecords, mce_poolsz;

Should order be also declared in this line? That way we can have all the
uninitialized 'int's together.

>  	struct gen_pool *tmpp;
>  	int ret = -ENOMEM;
> +	void *mce_pool;
> +	int order;
>  
> -	tmpp = gen_pool_create(ilog2(sizeof(struct mce_evt_llist)), -1);
> +	order = ilog2(sizeof(struct mce_evt_llist)) + 1;

I didn't exactly understand why a +1 is needed here. Do you have a
pointer to somewhere to help understand this?

Also, I think, a comment on top might be useful since this isn't obvious.

> +	tmpp = gen_pool_create(order, -1);
>  	if (!tmpp)
>  		goto out;
>  
> -	ret = gen_pool_add(tmpp, (unsigned long)gen_pool_buf, MCE_POOLSZ, -1);
> +	mce_numrecords = max(80, num_possible_cpus() * 4);

How about using MCE_MIN_ENTRIES here?

> +	mce_poolsz = mce_numrecords * (1 << order);
> +	mce_pool = kmalloc(mce_poolsz, GFP_KERNEL);
> +	if (!mce_pool) {
> +		gen_pool_destroy(tmpp);
> +		goto out;
> +	}
> +	ret = gen_pool_add(tmpp, (unsigned long)mce_pool, mce_poolsz, -1);
>  	if (ret) {
>  		gen_pool_destroy(tmpp);
>  		goto out;