From: David Hildenbrand <david@redhat.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
Mike Kravetz <mike.kravetz@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>,
mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
dave.hansen@linux.intel.com, luto@kernel.org,
Peter Zijlstra <peterz@infradead.org>,
viro@zeniv.linux.org.uk,
Andrew Morton <akpm@linux-foundation.org>,
paulmck@kernel.org, mchehab+huawei@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>,
Xiongchun duan <duanxiongchun@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 v7 05/15] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page()
Date: Wed, 9 Dec 2020 09:49:54 +0100 [thread overview]
Message-ID: <096ee806-b371-c22b-9066-8891935fbd5e@redhat.com> (raw)
In-Reply-To: <CAMZfGtWepk0EXc_fCtS83gvhfKpMrXxP8k3oWwfhWKmPJ3jjwA@mail.gmail.com>
On 09.12.20 08:36, Muchun Song wrote:
> On Mon, Dec 7, 2020 at 8:39 PM David Hildenbrand <david@redhat.com> wrote:
>>
>> On 30.11.20 16:18, Muchun Song wrote:
>>> In the later patch, we can use the free_vmemmap_page() to free the
>>> unused vmemmap pages and initialize a page for vmemmap page using
>>> via prepare_vmemmap_page().
>>>
>>> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>>> ---
>>> include/linux/bootmem_info.h | 24 ++++++++++++++++++++++++
>>> 1 file changed, 24 insertions(+)
>>>
>>> diff --git a/include/linux/bootmem_info.h b/include/linux/bootmem_info.h
>>> index 4ed6dee1adc9..239e3cc8f86c 100644
>>> --- a/include/linux/bootmem_info.h
>>> +++ b/include/linux/bootmem_info.h
>>> @@ -3,6 +3,7 @@
>>> #define __LINUX_BOOTMEM_INFO_H
>>>
>>> #include <linux/mmzone.h>
>>> +#include <linux/mm.h>
>>>
>>> /*
>>> * Types for free bootmem stored in page->lru.next. These have to be in
>>> @@ -22,6 +23,29 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat);
>>> void get_page_bootmem(unsigned long info, struct page *page,
>>> unsigned long type);
>>> void put_page_bootmem(struct page *page);
>>> +
>>> +static inline void free_vmemmap_page(struct page *page)
>>> +{
>>> + VM_WARN_ON(!PageReserved(page) || page_ref_count(page) != 2);
>>> +
>>> + /* bootmem page has reserved flag in the reserve_bootmem_region */
>>> + if (PageReserved(page)) {
>>> + unsigned long magic = (unsigned long)page->freelist;
>>> +
>>> + if (magic == SECTION_INFO || magic == MIX_SECTION_INFO)
>>> + put_page_bootmem(page);
>>> + else
>>> + WARN_ON(1);
>>> + }
>>> +}
>>> +
>>> +static inline void prepare_vmemmap_page(struct page *page)
>>> +{
>>> + unsigned long section_nr = pfn_to_section_nr(page_to_pfn(page));
>>> +
>>> + get_page_bootmem(section_nr, page, SECTION_INFO);
>>> + mark_page_reserved(page);
>>> +}
>>
>> Can you clarify in the description when exactly these functions are
>> called and on which type of pages?
>>
>> Would indicating "bootmem" in the function names make it clearer what we
>> are dealing with?
>>
>> E.g., any memory allocated via the memblock allocator and not via the
>> buddy will be makred reserved already in the memmap. It's unclear to me
>> why we need the mark_page_reserved() here - can you enlighten me? :)
>
> Sorry for ignoring this question. Because the vmemmap pages are allocated
> from the bootmem allocator which is marked as PG_reserved. For those bootmem
> pages, we should call put_page_bootmem for free. You can see that we
> clear the PG_reserved in the put_page_bootmem. In order to be consistent,
> the prepare_vmemmap_page also marks the page as PG_reserved.
I don't think that really makes sense.
After put_page_bootmem() put the last reference, it clears PG_reserved
and hands the page over to the buddy via free_reserved_page(). From that
point on, further get_page_bootmem() would be completely wrong and
dangerous.
Both, put_page_bootmem() and get_page_bootmem() rely on the fact that
they are dealing with memblock allcoations - marked via PG_reserved. If
prepare_vmemmap_page() would be called on something that's *not* coming
from the memblock allocator, it would be completely broken - or am I
missing something?
AFAIKT, there should rather be a BUG_ON(!PageReserved(page)) in
prepare_vmemmap_page() - or proper handling to deal with !memblock
allocations.
And as I said, indicating "bootmem" as part of the function names might
make it clearer that this is not for getting any vmemmap pages (esp.
allocated when hotplugging memory).
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-12-09 8:50 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-30 15:18 [PATCH v7 00/15] Free some vmemmap pages of hugetlb page Muchun Song
2020-11-30 15:18 ` [PATCH v7 01/15] mm/memory_hotplug: Move bootmem info registration API to bootmem_info.c Muchun Song
2020-12-07 12:12 ` David Hildenbrand
2020-11-30 15:18 ` [PATCH v7 02/15] mm/memory_hotplug: Move {get,put}_page_bootmem() " Muchun Song
2020-12-07 12:14 ` David Hildenbrand
2020-12-07 12:16 ` [External] " Muchun Song
2020-11-30 15:18 ` [PATCH v7 03/15] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP Muchun Song
2020-12-07 12:19 ` David Hildenbrand
2020-12-07 12:42 ` [External] " Muchun Song
2020-12-07 12:47 ` David Hildenbrand
2020-12-07 13:22 ` Muchun Song
2020-11-30 15:18 ` [PATCH v7 04/15] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate Muchun Song
2020-12-07 12:36 ` David Hildenbrand
2020-12-07 13:11 ` [External] " Muchun Song
2020-12-09 8:54 ` David Hildenbrand
2020-12-09 9:27 ` Muchun Song
2020-11-30 15:18 ` [PATCH v7 05/15] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() Muchun Song
2020-12-07 12:39 ` David Hildenbrand
2020-12-07 13:23 ` [External] " Muchun Song
2020-12-09 7:36 ` Muchun Song
2020-12-09 8:49 ` David Hildenbrand [this message]
2020-12-09 9:25 ` Muchun Song
2020-12-09 9:32 ` David Hildenbrand
2020-12-09 9:43 ` Muchun Song
2020-11-30 15:18 ` [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two Muchun Song
2020-12-09 9:57 ` David Hildenbrand
2020-12-09 10:03 ` [External] " Muchun Song
2020-12-09 10:06 ` David Hildenbrand
2020-12-09 10:10 ` David Hildenbrand
2020-12-09 10:16 ` Muchun Song
2020-12-09 15:13 ` Muchun Song
2020-12-09 15:47 ` David Hildenbrand
2020-12-09 15:50 ` Muchun Song
2020-12-09 10:10 ` Muchun Song
2020-11-30 15:18 ` [PATCH v7 07/15] x86/mm/64: Disable PMD page mapping of vmemmap Muchun Song
2020-11-30 15:18 ` [PATCH v7 08/15] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Muchun Song
2020-11-30 15:18 ` [PATCH v7 09/15] mm/hugetlb: Defer freeing of HugeTLB pages Muchun Song
2020-11-30 15:18 ` [PATCH v7 10/15] mm/hugetlb: Allocate the vmemmap pages associated with each hugetlb page Muchun Song
2020-11-30 15:18 ` [PATCH v7 11/15] mm/hugetlb: Set the PageHWPoison to the raw error page Muchun Song
2020-11-30 15:18 ` [PATCH v7 12/15] mm/hugetlb: Flush work when dissolving hugetlb page Muchun Song
2020-11-30 15:18 ` [PATCH v7 13/15] mm/hugetlb: Add a kernel parameter hugetlb_free_vmemmap Muchun Song
2020-12-04 0:01 ` Song Bao Hua (Barry Song)
2020-11-30 15:18 ` [PATCH v7 14/15] mm/hugetlb: Gather discrete indexes of tail page Muchun Song
2020-11-30 15:18 ` [PATCH v7 15/15] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page Muchun Song
2020-12-03 8:35 ` [PATCH v7 00/15] Free some vmemmap pages of hugetlb page Muchun Song
2020-12-03 23:48 ` Mike Kravetz
2020-12-04 3:39 ` [External] " Muchun Song
2020-12-07 18:38 ` Oscar Salvador
2020-12-08 2:26 ` Muchun Song
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