From: Michal Hocko <mhocko@suse.com>
To: Mike Kravetz <mike.kravetz@oracle.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Shakeel Butt <shakeelb@google.com>,
Oscar Salvador <osalvador@suse.de>,
David Hildenbrand <david@redhat.com>,
Muchun Song <songmuchun@bytedance.com>,
David Rientjes <rientjes@google.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Matthew Wilcox <willy@infradead.org>,
HORIGUCHI NAOYA <naoya.horiguchi@nec.com>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
Waiman Long <longman@redhat.com>, Peter Xu <peterx@redhat.com>,
Mina Almasry <almasrymina@google.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH 2/8] hugetlb: recompute min_count when dropping hugetlb_lock
Date: Tue, 23 Mar 2021 08:50:53 +0100 [thread overview]
Message-ID: <YFmd3d5B2VT4GkiG@dhcp22.suse.cz> (raw)
In-Reply-To: <a7d90d58-fa6a-7fa1-77c9-a08515746018@oracle.com>
On Mon 22-03-21 16:07:29, Mike Kravetz wrote:
> On 3/22/21 7:07 AM, Michal Hocko wrote:
> > On Fri 19-03-21 15:42:03, Mike Kravetz wrote:
> >> The routine set_max_huge_pages reduces the number of hugetlb_pages,
> >> by calling free_pool_huge_page in a loop. It does this as long as
> >> persistent_huge_pages() is above a calculated min_count value.
> >> However, this loop can conditionally drop hugetlb_lock and in some
> >> circumstances free_pool_huge_page can drop hugetlb_lock. If the
> >> lock is dropped, counters could change the calculated min_count
> >> value may no longer be valid.
> >
> > OK, this one looks like a real bug fix introduced by 55f67141a8927.
> > Unless I am missing something we could release pages which are reserved
> > already.
> >
> >> The routine try_to_free_low has the same issue.
> >>
> >> Recalculate min_count in each loop iteration as hugetlb_lock may have
> >> been dropped.
> >>
> >> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> >> ---
> >> mm/hugetlb.c | 25 +++++++++++++++++++++----
> >> 1 file changed, 21 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> >> index d5be25f910e8..c537274c2a38 100644
> >> --- a/mm/hugetlb.c
> >> +++ b/mm/hugetlb.c
> >> @@ -2521,11 +2521,20 @@ static void __init report_hugepages(void)
> >> }
> >> }
> >>
> >> +static inline unsigned long min_hp_count(struct hstate *h, unsigned long count)
> >> +{
> >> + unsigned long min_count;
> >> +
> >> + min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
> >> + return max(count, min_count);
> >
> > Just out of curiousity, is compiler allowed to inline this piece of code
> > and then cache the value? In other words do we need to make these
> > READ_ONCE or otherwise enforce the no-caching behavior?
>
> I honestly do not know if the compiler is allowed to do that. The
> assembly code generated by my compiler does not cache the value, but
> that does not guarantee anything. I can add READ_ONCE to make the
> function look something like:
>
> static inline unsigned long min_hp_count(struct hstate *h, unsigned long count)
> {
> unsigned long min_count;
>
> min_count = READ_ONCE(h->resv_huge_pages) + READ_ONCE(h->nr_huge_pages)
> - READ_ONCE(h->free_huge_pages);
> return max(count, min_count);
> }
Maybe just forcing to never inline the function should be sufficient.
This is not a hot path to micro optimize for no function call. But there
are much more qualified people on the CC list on this matter who could
clarify. Peter?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-03-23 7:51 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 22:42 [RFC PATCH 0/8] make hugetlb put_page safe for all calling contexts Mike Kravetz
2021-03-19 22:42 ` [RFC PATCH 1/8] hugetlb: add per-hstate mutex to synchronize user adjustments Mike Kravetz
2021-03-22 13:59 ` Michal Hocko
2021-03-22 16:57 ` Mike Kravetz
2021-03-23 7:48 ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 2/8] hugetlb: recompute min_count when dropping hugetlb_lock Mike Kravetz
2021-03-22 14:07 ` Michal Hocko
2021-03-22 23:07 ` Mike Kravetz
2021-03-23 7:50 ` Michal Hocko [this message]
2021-03-23 8:01 ` Peter Zijlstra
2021-03-23 8:14 ` Michal Hocko
2021-03-23 23:18 ` Mike Kravetz
2021-03-24 8:36 ` Michal Hocko
2021-03-24 16:43 ` Mike Kravetz
2021-03-19 22:42 ` [RFC PATCH 3/8] hugetlb: create remove_hugetlb_page() to separate functionality Mike Kravetz
2021-03-22 14:15 ` Michal Hocko
2021-03-22 17:01 ` Mike Kravetz
2021-03-19 22:42 ` [RFC PATCH 4/8] hugetlb: call update_and_free_page without hugetlb_lock Mike Kravetz
2021-03-22 14:19 ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 5/8] hugetlb: change free_pool_huge_page to remove_pool_huge_page Mike Kravetz
2021-03-22 14:31 ` Michal Hocko
2021-03-22 23:28 ` Mike Kravetz
2021-03-23 7:57 ` Michal Hocko
2021-03-24 1:03 ` Mike Kravetz
2021-03-24 8:40 ` Michal Hocko
2021-03-24 16:38 ` Mike Kravetz
2021-03-24 16:50 ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 6/8] hugetlb: make free_huge_page irq safe Mike Kravetz
2021-03-21 19:55 ` Mike Kravetz
2021-03-22 13:36 ` [hugetlb] cd190f60f9: BUG:sleeping_function_called_from_invalid_context_at_mm/hugetlb.c kernel test robot
2021-03-22 14:35 ` [RFC PATCH 6/8] hugetlb: make free_huge_page irq safe Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context Mike Kravetz
2021-03-22 8:41 ` Peter Zijlstra
2021-03-22 17:42 ` Mike Kravetz
2021-03-22 18:10 ` Roman Gushchin
2021-03-23 18:51 ` Mike Kravetz
2021-03-23 19:07 ` Roman Gushchin
2021-03-24 8:43 ` Michal Hocko
2021-03-24 16:53 ` Mike Kravetz
2021-03-22 20:43 ` Peter Zijlstra
2021-03-22 14:42 ` Michal Hocko
2021-03-22 14:46 ` Michal Hocko
2021-03-19 22:42 ` [RFC PATCH 8/8] hugetlb: track hugetlb pages allocated via cma_alloc Mike Kravetz
[not found] ` <20210320011857.2004-1-hdanton@sina.com>
2021-03-25 0:26 ` [RFC PATCH 7/8] hugetlb: add update_and_free_page_no_sleep for irq context Mike Kravetz
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