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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id p26sm3317403wmc.24.2020.02.25.01.57.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Feb 2020 01:57:13 -0800 (PST) Date: Tue, 25 Feb 2020 10:57:13 +0100 From: Michal Hocko To: Baoquan He Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, richardw.yang@linux.intel.com, david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com, rppt@linux.ibm.com, robin.murphy@arm.com Subject: Re: [PATCH v2 4/7] mm/sparse.c: only use subsection map in VMEMMAP case Message-ID: <20200225095713.GL22443@dhcp22.suse.cz> References: <20200220043316.19668-1-bhe@redhat.com> <20200220043316.19668-5-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200220043316.19668-5-bhe@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 20-02-20 12:33:13, Baoquan He wrote: > Currently, subsection map is used when SPARSEMEM is enabled, including > VMEMMAP case and !VMEMMAP case. However, subsection hotplug is not > supported at all in SPARSEMEM|!VMEMMAP case, subsection map is unnecessary > and misleading. Let's adjust code to only allow subsection map being > used in VMEMMAP case. This really needs more explanation I believe. What exactly happens if somebody tries to hotremove a part of the section with !VMEMMAP? I can see that clear_subsection_map returns 0 but that is not an error code. Besides that section_deactivate doesn't propagate the error upwards. /me stares into the code OK, I can see it now. It is relying on check_pfn_span to use the proper subsection granularity. This really begs for a comment in the code somewhere. > > Signed-off-by: Baoquan He > --- > include/linux/mmzone.h | 2 ++ > mm/sparse.c | 20 ++++++++++++++++++++ > 2 files changed, 22 insertions(+) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 462f6873905a..fc0de3a9a51e 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1185,7 +1185,9 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec) > #define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK) > > struct mem_section_usage { > +#ifdef CONFIG_SPARSEMEM_VMEMMAP > DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION); > +#endif > /* See declaration of similar field in struct zone */ > unsigned long pageblock_flags[0]; > }; > diff --git a/mm/sparse.c b/mm/sparse.c > index df857ee9330c..66c497d6a229 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -209,6 +209,7 @@ static inline unsigned long first_present_section_nr(void) > return next_present_section_nr(-1); > } > > +#ifdef CONFIG_SPARSEMEM_VMEMMAP > static void subsection_mask_set(unsigned long *map, unsigned long pfn, > unsigned long nr_pages) > { > @@ -243,6 +244,11 @@ void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages) > nr_pages -= pfns; > } > } > +#else > +void __init subsection_map_init(unsigned long pfn, unsigned long nr_pages) > +{ > +} > +#endif > > /* Record a memory area against a node. */ > void __init memory_present(int nid, unsigned long start, unsigned long end) > @@ -726,6 +732,7 @@ static void free_map_bootmem(struct page *memmap) > } > #endif /* CONFIG_SPARSEMEM_VMEMMAP */ > > +#ifdef CONFIG_SPARSEMEM_VMEMMAP > /** > * clear_subsection_map - Clear subsection map of one memory region > * > @@ -764,6 +771,12 @@ static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages) > > return 1; > } > +#else > +static int clear_subsection_map(unsigned long pfn, unsigned long nr_pages) > +{ > + return 0; > +} > +#endif > > static void section_deactivate(unsigned long pfn, unsigned long nr_pages, > struct vmem_altmap *altmap) > @@ -820,6 +833,7 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, > ms->section_mem_map = (unsigned long)NULL; > } > > +#ifdef CONFIG_SPARSEMEM_VMEMMAP > /** > * fill_subsection_map - fill subsection map of a memory region > * @pfn - start pfn of the memory range > @@ -854,6 +868,12 @@ static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages) > > return rc; > } > +#else > +static int fill_subsection_map(unsigned long pfn, unsigned long nr_pages) > +{ > + return 0; > +} > +#endif > > static struct page * __meminit section_activate(int nid, unsigned long pfn, > unsigned long nr_pages, struct vmem_altmap *altmap) > -- > 2.17.2 > -- Michal Hocko SUSE Labs