lkml.org 
[lkml]   [2021]   [Oct]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 1/5] hugetlb: add demote hugetlb page sysfs interfaces
On 2021-10-01 19:52, Mike Kravetz wrote:
> +static int demote_pool_huge_page(struct hstate *h, nodemask_t
> *nodes_allowed)
> + __must_hold(&hugetlb_lock)
> +{
> + int rc = 0;
> +
> + lockdep_assert_held(&hugetlb_lock);
> +
> + /* We should never get here if no demote order */
> + if (!h->demote_order)
> + return rc;

Probably add a warning here? If we should never reach this but we do,
then
something got screwed along the way and we might want to know.

> +static ssize_t demote_store(struct kobject *kobj,
> + struct kobj_attribute *attr, const char *buf, size_t len)
> +{
> + unsigned long nr_demote;
> + unsigned long nr_available;
> + nodemask_t nodes_allowed, *n_mask;
> + struct hstate *h;
> + int err;
> + int nid;
> +
> + err = kstrtoul(buf, 10, &nr_demote);
> + if (err)
> + return err;
> + h = kobj_to_hstate(kobj, &nid);
> +
> + /* Synchronize with other sysfs operations modifying huge pages */
> + mutex_lock(&h->resize_lock);
> +
> + spin_lock_irq(&hugetlb_lock);
> + if (nid != NUMA_NO_NODE) {
> + init_nodemask_of_node(&nodes_allowed, nid);
> + n_mask = &nodes_allowed;
> + } else {
> + n_mask = &node_states[N_MEMORY];
> + }

Cannot the n_mask dance be outside the locks? That does not need to be
protected, right?

> +
> + while (nr_demote) {
> + /*
> + * Check for available pages to demote each time thorough the
> + * loop as demote_pool_huge_page will drop hugetlb_lock.
> + *
> + * NOTE: demote_pool_huge_page does not yet drop hugetlb_lock
> + * but will when full demote functionality is added in a later
> + * patch.
> + */
> + if (nid != NUMA_NO_NODE)
> + nr_available = h->free_huge_pages_node[nid];
> + else
> + nr_available = h->free_huge_pages;
> + nr_available -= h->resv_huge_pages;
> + if (!nr_available)
> + break;
> +
> + if (!demote_pool_huge_page(h, n_mask))
> + break;

Is it possible that when demote_pool_huge_page() drops the lock,
h->resv_huge_pages change? Or that can only happen under h->resize_lock?

> +
> + nr_demote--;
> + }
> +
> + spin_unlock_irq(&hugetlb_lock);
> + mutex_unlock(&h->resize_lock);
> +
> + return len;
> +}
> +HSTATE_ATTR_WO(demote);
> +
> +static ssize_t demote_size_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + struct hstate *h;
> + unsigned long demote_size;
> + int nid;
> +
> + h = kobj_to_hstate(kobj, &nid);
> + demote_size = h->demote_order;

This has already been pointed out.

> +
> + return sysfs_emit(buf, "%lukB\n",
> + (unsigned long)(PAGE_SIZE << h->demote_order) / SZ_1K);
> +}
> +
> +static ssize_t demote_size_store(struct kobject *kobj,
> + struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct hstate *h, *t_hstate;
> + unsigned long demote_size;
> + unsigned int demote_order;
> + int nid;

This is just a nit-pick, but what is t_hstate? demote_hstate might be
more descriptive.

> +
> + demote_size = (unsigned long)memparse(buf, NULL);
> +
> + t_hstate = size_to_hstate(demote_size);
> + if (!t_hstate)
> + return -EINVAL;
> + demote_order = t_hstate->order;
> +
> + /* demote order must be smaller hstate order */

"must be smaller than"

--
Oscar Salvador
SUSE Labs

\
 
 \ /
  Last update: 2021-10-05 10:24    [W:1.441 / U:0.088 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site