From: David Hildenbrand <dhildenb@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: David Hildenbrand <david@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH v1 2/2] mm: factor out next_present_section_nr()
Date: Mon, 13 Jan 2020 17:57:12 -0500 (EST) [thread overview]
Message-ID: <0B77E39C-BD38-4A61-AB28-3578B519952F@redhat.com> (raw)
In-Reply-To: <20200113224155.efoekgw4hyey2by2@box>
> Am 13.01.2020 um 23:41 schrieb Kirill A. Shutemov <kirill@shutemov.name>:
>
> On Mon, Jan 13, 2020 at 03:40:35PM +0100, David Hildenbrand wrote:
>> Let's move it to the header and use the shorter variant from
>> mm/page_alloc.c (the original one will also check
>> "__highest_present_section_nr + 1", which is not necessary). While at it,
>> make the section_nr in next_pfn() const.
>>
>> In next_pfn(), we now return section_nr_to_pfn(-1) instead of -1 once
>> we exceed __highest_present_section_nr, which doesn't make a difference in
>> the caller as it is big enough (>= all sane end_pfn).
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Michal Hocko <mhocko@kernel.org>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Cc: Kirill A. Shutemov <kirill@shutemov.name>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>> include/linux/mmzone.h | 10 ++++++++++
>> mm/page_alloc.c | 11 ++---------
>> mm/sparse.c | 10 ----------
>> 3 files changed, 12 insertions(+), 19 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index c2bc309d1634..462f6873905a 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -1379,6 +1379,16 @@ static inline int pfn_present(unsigned long pfn)
>> return present_section(__nr_to_section(pfn_to_section_nr(pfn)));
>> }
>>
>> +static inline unsigned long next_present_section_nr(unsigned long section_nr)
>> +{
>> + while (++section_nr <= __highest_present_section_nr) {
>> + if (present_section_nr(section_nr))
>> + return section_nr;
>> + }
>> +
>> + return -1;
>> +}
>> +
>> /*
>> * These are _only_ used during initialisation, therefore they
>> * can use __initdata ... They could have names to indicate
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index a92791512077..26e8044e9848 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5852,18 +5852,11 @@ overlap_memmap_init(unsigned long zone, unsigned long *pfn)
>> /* Skip PFNs that belong to non-present sections */
>> static inline __meminit unsigned long next_pfn(unsigned long pfn)
>> {
>> - unsigned long section_nr;
>> + const unsigned long section_nr = pfn_to_section_nr(++pfn);
>>
>> - section_nr = pfn_to_section_nr(++pfn);
>> if (present_section_nr(section_nr))
>> return pfn;
>> -
>> - while (++section_nr <= __highest_present_section_nr) {
>> - if (present_section_nr(section_nr))
>> - return section_nr_to_pfn(section_nr);
>> - }
>> -
>> - return -1;
>> + return section_nr_to_pfn(next_present_section_nr(section_nr));
>
> This changes behaviour in the corner case: if next_present_section_nr()
> returns -1, we call section_nr_to_pfn() for it. It's unlikely would give
> any valid pfn, but I can't say for sure for all archs. I guess the worst
> case scenrio would be endless loop over the same secitons/pfns.
>
> Have you considered the case?
Yes, see the patch description. We return -1 << PFN_SECTION_SHIFT, so a number close to the end of the address space (0xfff...000). (Will double check tomorrow if any 32bit arch could be problematic here)
Thanks!
>
> --
> Kirill A. Shutemov
>
next prev parent reply other threads:[~2020-01-13 22:57 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 14:40 [PATCH v1 0/2] mm/page_alloc: memmap_init_zone() cleanups David Hildenbrand
2020-01-13 14:40 ` [PATCH v1 1/2] mm/page_alloc: fix and rework pfn handling in memmap_init_zone() David Hildenbrand
2020-02-03 21:35 ` Alexander Duyck
2020-02-03 21:44 ` David Hildenbrand
2020-02-03 23:17 ` Alexander Duyck
2020-02-04 8:40 ` David Hildenbrand
2020-01-13 14:40 ` [PATCH v1 2/2] mm: factor out next_present_section_nr() David Hildenbrand
2020-01-13 22:41 ` Kirill A. Shutemov
2020-01-13 22:57 ` David Hildenbrand [this message]
2020-01-13 23:02 ` David Hildenbrand
2020-01-14 10:41 ` Kirill A. Shutemov
2020-01-14 10:49 ` David Hildenbrand
2020-01-14 15:52 ` Kirill A. Shutemov
2020-01-14 16:50 ` David Hildenbrand
2020-01-14 16:52 ` David Hildenbrand
2020-01-31 4:30 ` [PATCH v1 0/2] mm/page_alloc: memmap_init_zone() cleanups Andrew Morton
2020-02-03 14:49 ` Kirill A. Shutemov
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