Re: [PATCH 5/5] mm/hugetl.c: warn out if expected count of huge pages adjustment is not achieved

[Baoquan He]

Hi Mike,

On 07/20/20 at 05:38pm, Mike Kravetz wrote:
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 467894d8332a..1dfb5d9e4e06 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -2661,7 +2661,7 @@ static int adjust_pool_surplus(struct hstate *h, 
> > nodemask_t *nodes_allowed,
> >  static int set_max_huge_pages(struct hstate *h, unsigned long count, int 
> > nid,
> >                           nodemask_t *nodes_allowed)
> >  {
> > -   unsigned long min_count, ret;
> > +   unsigned long min_count, ret, old_max;
> >     NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
> >  
> >     /*
> > @@ -2723,6 +2723,7 @@ static int set_max_huge_pages(struct hstate *h, 
> > unsigned long count, int nid,
> >      * pool might be one hugepage larger than it needs to be, but
> >      * within all the constraints specified by the sysctls.
> >      */
> > +   old_max = persistent_huge_pages(h);
> >     while (h->surplus_huge_pages && count > persistent_huge_pages(h)) {
> >             if (!adjust_pool_surplus(h, nodes_allowed, -1))
> >                     break;
> > @@ -2779,6 +2780,16 @@ static int set_max_huge_pages(struct hstate *h, 
> > unsigned long count, int nid,
> >     }
> >  out:
> >     h->max_huge_pages = persistent_huge_pages(h);
> > +   if (count != h->max_huge_pages) {
> > +           char buf[32];
> > +
> > +           string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
> > +           pr_warn("HugeTLB: %s %lu of page size %s failed. Only %s %lu 
> > hugepages.\n",
> > +                   count > old_max ? "increasing" : "decreasing",
> > +                   abs(count - old_max), buf,
> > +                   count > old_max ? "increased" : "decreased",
> > +                   abs(old_max - h->max_huge_pages));
> > +   }
> >     spin_unlock(&hugetlb_lock);
> 
> I would prefer if we drop the lock before logging the message.  That would
> involve grabbing the value of h->max_huge_pages before dropping the lock.

Do you think the below change is OK to you to move the message logging
after lock dropping? If yes, I will repost with updated patches.

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6a9b7556ce5b..b5aa32a13569 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2661,7 +2661,7 @@ static int adjust_pool_surplus(struct hstate *h, 
nodemask_t *nodes_allowed,
 static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
                              nodemask_t *nodes_allowed)
 {
-       unsigned long min_count, ret, old_max;
+       unsigned long min_count, ret, old_max, new_max;
        NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
 
        /*
@@ -2780,7 +2780,10 @@ static int set_max_huge_pages(struct hstate *h, unsigned 
long count, int nid,
        }
 out:
        h->max_huge_pages = persistent_huge_pages(h);
-       if (count != h->max_huge_pages) {
+       new_max = h->max_huge_pages;
+       spin_unlock(&hugetlb_lock);
+
+       if (count != new_max) {
                char buf[32];
 
                string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, 32);
@@ -2788,9 +2791,8 @@ static int set_max_huge_pages(struct hstate *h, unsigned 
long count, int nid,
                        count > old_max ? "increasing" : "decreasing",
                        abs(count - old_max), buf,
                        count > old_max ? "increased" : "decreased",
-                       abs(old_max - h->max_huge_pages));
+                       abs(old_max - new_max));
        }
-       spin_unlock(&hugetlb_lock);
 
        NODEMASK_FREE(node_alloc_noretry);