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Tue, 08 Dec 2020 23:37:20 -0800 (PST) MIME-Version: 1.0 References: <20201130151838.11208-1-songmuchun@bytedance.com> <20201130151838.11208-6-songmuchun@bytedance.com> <17abb7bb-de39-7580-b020-faec58032de9@redhat.com> In-Reply-To: <17abb7bb-de39-7580-b020-faec58032de9@redhat.com> From: Muchun Song Date: Wed, 9 Dec 2020 15:36:41 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v7 05/15] mm/bootmem_info: Introduce {free,prepare}_vmemmap_page() To: David Hildenbrand Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , Michal Hocko , "Song Bao Hua (Barry Song)" , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" 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, Dec 7, 2020 at 8:39 PM David Hildenbrand 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 > > --- > > 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 > > +#include > > > > /* > > * 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. Thanks. > > -- > Thanks, > > David / dhildenb > -- Yours, Muchun