From: Muchun Song <songmuchun@bytedance.com>
To: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
David Hildenbrand <david@redhat.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Liu Shixin <liushixin2@huawei.com>,
Yang Shi <shy828301@gmail.com>,
Oscar Salvador <osalvador@suse.de>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH v2 1/9] mm/hugetlb: remove checking hstate_is_gigantic() in return_unused_surplus_pages()
Date: Fri, 24 Jun 2022 16:03:42 +0800 [thread overview]
Message-ID: <YrVv3gKMxbu/dwCs@FVFYT0MHHV2J.usts.net> (raw)
In-Reply-To: <0b69e3ef-0123-4575-b68d-4d9b2067aa0e@huawei.com>
On Fri, Jun 24, 2022 at 10:25:48AM +0800, Miaohe Lin wrote:
> On 2022/6/24 7:51, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> >
> > I found a weird state of 1GB hugepage pool, caused by the following
> > procedure:
> >
> > - run a process reserving all free 1GB hugepages,
> > - shrink free 1GB hugepage pool to zero (i.e. writing 0 to
> > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages), then
> > - kill the reserving process.
> >
> > , then all the hugepages are free *and* surplus at the same time.
> >
> > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
> > 3
> > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/free_hugepages
> > 3
> > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/resv_hugepages
> > 0
> > $ cat /sys/kernel/mm/hugepages/hugepages-1048576kB/surplus_hugepages
> > 3
> >
> > This state is resolved by reserving and allocating the pages then
> > freeing them again, so this seems not to result in serious problem.
> > But it's a little surprizing (shrinking pool suddenly fails).
> >
> > This behavior is caused by hstate_is_gigantic() check in
> > return_unused_surplus_pages(). This was introduced so long ago in 2008
> > by commit aa888a74977a ("hugetlb: support larger than MAX_ORDER"), and
> > it seems to me that this check is no longer unnecessary. Let's remove it.
>
> s/unnecessary/necessary/
>
> >
> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> > ---
> > mm/hugetlb.c | 4 ----
> > 1 file changed, 4 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index a57e1be41401..c538278170a2 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -2432,10 +2432,6 @@ static void return_unused_surplus_pages(struct hstate *h,
> > /* Uncommit the reservation */
> > h->resv_huge_pages -= unused_resv_pages;
> >
> > - /* Cannot return gigantic pages currently */
> > - if (hstate_is_gigantic(h))
> > - goto out;
> > -
>
> IIUC it might be better to do the below check:
> /*
> * Cannot return gigantic pages currently if runtime gigantic page
> * allocation is not supported.
> */
> if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
> goto out;
>
The change looks good to me. However, the comments above is unnecessary
since gigantic_page_runtime_supported() is straightforward.
Thanks.
> But I might be miss something.
>
> Thanks.
>
> > /*
> > * Part (or even all) of the reservation could have been backed
> > * by pre-allocated pages. Only free surplus pages.
> >
>
>
next prev parent reply other threads:[~2022-06-24 8:03 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-23 23:51 [PATCH v2 0/9] mm, hwpoison: enable 1GB hugepage support (v2) Naoya Horiguchi
2022-06-23 23:51 ` [PATCH v2 1/9] mm/hugetlb: remove checking hstate_is_gigantic() in return_unused_surplus_pages() Naoya Horiguchi
2022-06-24 2:25 ` Miaohe Lin
2022-06-24 8:03 ` Muchun Song [this message]
2022-06-24 8:15 ` Miaohe Lin
2022-06-24 8:34 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-24 19:11 ` Mike Kravetz
2022-06-27 6:02 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-27 17:25 ` Mike Kravetz
2022-06-28 3:01 ` Miaohe Lin
2022-06-28 8:38 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-30 2:27 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-23 23:51 ` [PATCH v2 2/9] mm/hugetlb: separate path for hwpoison entry in copy_hugetlb_page_range() Naoya Horiguchi
2022-06-24 9:23 ` Miaohe Lin
2022-06-27 6:06 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-24 20:57 ` Mike Kravetz
2022-06-27 6:48 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-27 7:57 ` Muchun Song
2022-06-23 23:51 ` [PATCH v2 3/9] mm/hugetlb: make pud_huge() and huge_pud() aware of non-present pud entry Naoya Horiguchi
2022-06-24 8:40 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-25 0:02 ` Mike Kravetz
2022-06-27 7:07 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-25 9:42 ` Miaohe Lin
2022-06-27 7:24 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-23 23:51 ` [PATCH v2 4/9] mm, hwpoison, hugetlb: support saving mechanism of raw error pages Naoya Horiguchi
2022-06-27 3:16 ` Miaohe Lin
2022-06-27 7:56 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-27 9:26 ` Muchun Song
2022-06-28 2:41 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-28 6:26 ` Muchun Song
2022-06-28 7:51 ` Muchun Song
2022-06-28 8:17 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-28 10:37 ` Muchun Song
2022-06-23 23:51 ` [PATCH v2 5/9] mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage Naoya Horiguchi
2022-06-27 8:32 ` Miaohe Lin
2022-06-27 11:48 ` Miaohe Lin
2022-06-23 23:51 ` [PATCH v2 6/9] mm, hwpoison: set PG_hwpoison for busy hugetlb pages Naoya Horiguchi
2022-06-27 8:39 ` Miaohe Lin
2022-06-23 23:51 ` [PATCH v2 7/9] mm, hwpoison: make __page_handle_poison returns int Naoya Horiguchi
2022-06-27 9:02 ` Miaohe Lin
2022-06-28 6:02 ` HORIGUCHI NAOYA(堀口 直也)
2022-06-23 23:51 ` [PATCH v2 8/9] mm, hwpoison: skip raw hwpoison page in freeing 1GB hugepage Naoya Horiguchi
2022-06-27 12:24 ` Miaohe Lin
2022-06-23 23:51 ` [PATCH v2 9/9] mm, hwpoison: enable memory error handling on " Naoya Horiguchi
2022-06-28 2:06 ` Miaohe Lin
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