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Shutemov" To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Michal Hocko , Oscar Salvador Subject: Re: [PATCH v1 2/2] mm: factor out next_present_section_nr() Message-ID: <20200113224155.efoekgw4hyey2by2@box> References: <20200113144035.10848-1-david@redhat.com> <20200113144035.10848-3-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200113144035.10848-3-david@redhat.com> User-Agent: NeoMutt/20180716 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > Cc: Michal Hocko > Cc: Oscar Salvador > Cc: Kirill A. Shutemov > Signed-off-by: David Hildenbrand > --- > 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? -- Kirill A. Shutemov