linux-kernel - Re: [PATCH -V3 3/4] acpi, hmat: calculate abstract distance with HMAT

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Date:   Tue, 19 Sep 2023 15:14:10 +1000
From:   Alistair Popple <apopple@...dia.com>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Bharata B Rao <bharata@....com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Wei Xu <weixugc@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Michal Hocko <mhocko@...nel.org>,
        Yang Shi <shy828301@...il.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Rafael J Wysocki <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH -V3 3/4] acpi, hmat: calculate abstract distance with HMAT


Thanks for making changes here, looks better to me at least.

Huang Ying <ying.huang@...el.com> writes:

>  static __init void hmat_free_structures(void)
>  {
>  	struct memory_target *target, *tnext;
> @@ -801,6 +857,7 @@ static __init int hmat_init(void)
>  	struct acpi_table_header *tbl;
>  	enum acpi_hmat_type i;
>  	acpi_status status;
> +	int usage;
>  
>  	if (srat_disabled() || hmat_disable)
>  		return 0;
> @@ -841,7 +898,10 @@ static __init int hmat_init(void)
>  	hmat_register_targets();
>  
>  	/* Keep the table and structures if the notifier may use them */
> -	if (!hotplug_memory_notifier(hmat_callback, HMAT_CALLBACK_PRI))
> +	usage = !hotplug_memory_notifier(hmat_callback, HMAT_CALLBACK_PRI);
> +	if (!hmat_set_default_dram_perf())
> +		usage += !register_mt_adistance_algorithm(&hmat_adist_nb);
> +	if (usage)
>  		return 0;

Can we simplify the error handling here? As I understand it
hotplug_memory_notifier() and register_mt_adistance_algorithm() aren't
expected to ever fail because hmat_init() should only be called once and
the notifier register shouldn't fail. So wouldn't the below be
effectively the same thing but clearer?

    if (hotplug_memory_notifier(hmat_callback, HMAT_CALLBACK_PRI))
        goto out_put;
       
    if (!hmat_set_default_dram_perf())
        register_mt_adistance_algorithm(&hmat_adist_nb);

    return 0;

>  out_put:
>  	hmat_free_structures();

Also as an aside while looking at this patch I noticed a minor bug:

	status = acpi_get_table(ACPI_SIG_HMAT, 0, &tbl);
	if (ACPI_FAILURE(status))
		goto out_put;

This will call acpi_put_table(tbl) even though we failed to get the
table.