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

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Date:   Tue, 21 Jul 2020 17:55:20 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH 5/5] mm/hugetl.c: warn out if expected count of huge
 pages adjustment is not achieved

On 07/20/20 at 05:38pm, Mike Kravetz wrote:
> On 7/19/20 11:26 PM, Baoquan He wrote:
> > A customer complained that no any message is printed out when failed to
> > allocate explicitly specified number of persistent huge pages. That
> > specifying can be done by writing into /proc/sys/vm/nr_hugepages to
> > increase the persisten huge pages.
> > 
> > In the current code, it takes the best effort way to allocate the expected
> > number of huge pages. If only succeeding to get part of them, no any
> > information is printed out.
> > 
> > Here try to send out warning message if the expected number of huge pages
> > adjustment is not achieved, including increasing and decreasing the count
> > of persistent huge pages.
> 
> Perhaps change the wording a bit,
> 
> A customer complained that no message is logged when the number of
> persistent huge pages is not changed to the exact value written to
> the sysfs or proc nr_hugepages file.
> 
> In the current code, a best effort is made to satisfy requests made
> via the nr_hugepages file.  However, requests may be only partially
> satisfied.
> 
> Log a message if the code was unsuccessful in fully satisfying a
> request.  This includes both increasing and decreasing the number
> of persistent huge pages.

Thanks, sounds much better, I will use these to replace the old log.

> 
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  mm/hugetlb.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> I am not opposed to this patch.  However, I believe the best way for a user
> to determine if their request was successful is to compare the value of
> nr_hugepages to the value which was written.

Agree. While from our customer's request, they told the log can help
'Easily detect and analyse previous reservation failures'.

> 
> > 
> > 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.

Sure, will change. We should try to release the lock's burden. Thanks.