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

Sohil Mehta
2024-02-29T01:56:31Z

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;