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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.
> > 
> 
> 


  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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