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

From: Naik, Avadhut
Date: Mon Mar 11 2024 - 01:39:00 EST




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