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From: Muchun Song <songmuchun@bytedance.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "Jonathan Corbet" <corbet@lwn.net>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	bp@alien8.de, "X86 ML" <x86@kernel.org>,
	hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	paulmck@kernel.org, pawan.kumar.gupta@linux.intel.com,
	"Randy Dunlap" <rdunlap@infradead.org>,
	oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de,
	"Mina Almasry" <almasrymina@google.com>,
	"David Rientjes" <rientjes@google.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Oscar Salvador" <osalvador@suse.de>,
	"Michal Hocko" <mhocko@suse.com>,
	"Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	"David Hildenbrand" <david@redhat.com>,
	"HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>,
	"Joao Martins" <joao.m.martins@oracle.com>,
	"Xiongchun duan" <duanxiongchun@bytedance.com>,
	fam.zheng@bytedance.com, linux-doc@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	"Linux Memory Management List" <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [External] Re: [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages
Date: Sat, 17 Apr 2021 12:13:17 +0800
Message-ID: <CAMZfGtWXpTfeHeuHJdX5hjd03sNabZeh7Uzw7sPqgOFCWQDDZA@mail.gmail.com> (raw)
In-Reply-To: <33a4f2fe-72c2-a3a1-9205-461ddde9b162@oracle.com>

On Sat, Apr 17, 2021 at 7:56 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 4/15/21 1:40 AM, Muchun Song wrote:
> > In the subsequent patch, we should allocate the vmemmap pages when
> > freeing a HugeTLB page. But update_and_free_page() can be called
> > under any context, so we cannot use GFP_KERNEL to allocate vmemmap
> > pages. However, we can defer the actual freeing in a kworker to
> > prevent from using GFP_ATOMIC to allocate the vmemmap pages.
>
> Thanks!  I knew we would need to introduce a kworker for this when I
> removed the kworker previously used in free_huge_page.

Yeah, but another choice is using GFP_ATOMIC to allocate vmemmap
pages when we are in an atomic context. If not atomic context, just
use GFP_KERNEL. In this case, we can drop kworker.

>
> > The __update_and_free_page() is where the call to allocate vmemmmap
> > pages will be inserted.
>
> This patch adds the functionality required for __update_and_free_page
> to potentially sleep and fail.  More questions will come up in the
> subsequent patch when code must deal with the failures.

Right. More questions are welcome.

>
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > ---
> >  mm/hugetlb.c         | 73 ++++++++++++++++++++++++++++++++++++++++++++++++----
> >  mm/hugetlb_vmemmap.c | 12 ---------
> >  mm/hugetlb_vmemmap.h | 17 ++++++++++++
> >  3 files changed, 85 insertions(+), 17 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 923d05e2806b..eeb8f5480170 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1376,7 +1376,7 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
> >       h->nr_huge_pages_node[nid]--;
> >  }
> >
> > -static void update_and_free_page(struct hstate *h, struct page *page)
> > +static void __update_and_free_page(struct hstate *h, struct page *page)
> >  {
> >       int i;
> >       struct page *subpage = page;
> > @@ -1399,12 +1399,73 @@ static void update_and_free_page(struct hstate *h, struct page *page)
> >       }
> >  }
> >
> > +/*
> > + * As update_and_free_page() can be called under any context, so we cannot
> > + * use GFP_KERNEL to allocate vmemmap pages. However, we can defer the
> > + * actual freeing in a workqueue to prevent from using GFP_ATOMIC to allocate
> > + * the vmemmap pages.
> > + *
> > + * free_hpage_workfn() locklessly retrieves the linked list of pages to be
> > + * freed and frees them one-by-one. As the page->mapping pointer is going
> > + * to be cleared in free_hpage_workfn() anyway, it is reused as the llist_node
> > + * structure of a lockless linked list of huge pages to be freed.
> > + */
> > +static LLIST_HEAD(hpage_freelist);
> > +
> > +static void free_hpage_workfn(struct work_struct *work)
> > +{
> > +     struct llist_node *node;
> > +
> > +     node = llist_del_all(&hpage_freelist);
> > +
> > +     while (node) {
> > +             struct page *page;
> > +             struct hstate *h;
> > +
> > +             page = container_of((struct address_space **)node,
> > +                                  struct page, mapping);
> > +             node = node->next;
> > +             page->mapping = NULL;
> > +             h = page_hstate(page);
>
> The VM_BUG_ON_PAGE(!PageHuge(page), page) in page_hstate is going to
> trigger because a previous call to remove_hugetlb_page() will
> set_compound_page_dtor(page, NULL_COMPOUND_DTOR)

Sorry, I did not realise that. Thanks for your reminder.

>
> Note how h(hstate) is grabbed before calling update_and_free_page in
> existing code.
>
> We could potentially drop the !PageHuge(page) in page_hstate.  Or,
> perhaps just use 'size_to_hstate(page_size(page))' in free_hpage_workfn.

I prefer not to change the behavior of page_hstate(). So I
should use 'size_to_hstate(page_size(page))' directly.

Thanks Mike.


> --
> Mike Kravetz

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15  8:39 [PATCH v20 0/9] Free some vmemmap pages of HugeTLB page Muchun Song
2021-04-15  8:39 ` [PATCH v20 1/9] mm: memory_hotplug: factor out bootmem core functions to bootmem_info.c Muchun Song
2021-04-15  8:39 ` [PATCH v20 2/9] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2021-04-15  8:39 ` [PATCH v20 3/9] mm: hugetlb: gather discrete indexes of tail page Muchun Song
2021-04-16 18:54   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 4/9] mm: hugetlb: free the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-16 21:10   ` Mike Kravetz
2021-04-17  2:55     ` [External] " Muchun Song
2021-04-15  8:40 ` [PATCH v20 5/9] mm: hugetlb: defer freeing of HugeTLB pages Muchun Song
2021-04-16 23:55   ` Mike Kravetz
2021-04-17  4:13     ` Muchun Song [this message]
2021-04-15  8:40 ` [PATCH v20 6/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Muchun Song
2021-04-19 23:19   ` Mike Kravetz
2021-04-20  8:46     ` [External] " Muchun Song
2021-04-20 17:48       ` Mike Kravetz
2021-04-21  3:42         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 7/9] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Muchun Song
2021-04-19 23:41   ` Mike Kravetz
2021-04-15  8:40 ` [PATCH v20 8/9] mm: memory_hotplug: disable memmap_on_memory when hugetlb_free_vmemmap enabled Muchun Song
2021-04-20 10:35   ` Oscar Salvador
2021-04-21  3:41     ` [External] " Muchun Song
2021-04-21  7:33       ` Oscar Salvador
2021-04-21  9:06         ` Muchun Song
2021-04-15  8:40 ` [PATCH v20 9/9] mm: hugetlb: introduce nr_free_vmemmap_pages in the struct hstate Muchun Song

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