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    SubjectRe: [PATCH 04/14] mm, memory_hotplug: get rid of is_zone_device_section
    On Mon, May 15, 2017 at 4:58 PM, Michal Hocko <mhocko@kernel.org> wrote:
    > From: Michal Hocko <mhocko@suse.com>
    >
    > device memory hotplug hooks into regular memory hotplug only half way.
    > It needs memory sections to track struct pages but there is no
    > need/desire to associate those sections with memory blocks and export
    > them to the userspace via sysfs because they cannot be onlined anyway.
    >
    > This is currently expressed by for_device argument to arch_add_memory
    > which then makes sure to associate the given memory range with
    > ZONE_DEVICE. register_new_memory then relies on is_zone_device_section
    > to distinguish special memory hotplug from the regular one. While this
    > works now, later patches in this series want to move __add_zone outside
    > of arch_add_memory path so we have to come up with something else.
    >
    > Add want_memblock down the __add_pages path and use it to control
    > whether the section->memblock association should be done. arch_add_memory
    > then just trivially want memblock for everything but for_device hotplug.
    >
    > remove_memory_section doesn't need is_zone_device_section either. We can
    > simply skip all the memblock specific cleanup if there is no memblock
    > for the given section.
    >
    > This shouldn't introduce any functional change.
    >

    Hmm... one question about the memory_block behavior.

    In case one memory_block contains more than one memory section.
    If one section is "device zone", the whole memory_block is not visible
    in sysfs. Or until the whole memory_block is full, the sysfs is visible.

    This is the known behavior right?

    And in this case, the memory_block could be found. Would this introduce
    some problem when remove_memory_section()?


    > Changes since v1
    > - return 0 if want_memblock == 0 from __add_section as per Jerome Glisse
    >
    > Changes since v2
    > - fix remove_memory_section unlock on find_memory_block failure
    > as per Jerome - spotted by Evgeny Baskakov
    >
    > Tested-by: Dan Williams <dan.j.williams@intel.com>
    > Acked-by: Vlastimil Babka <vbabka@suse.cz>
    > Signed-off-by: Michal Hocko <mhocko@suse.com>
    > ---
    > arch/ia64/mm/init.c | 2 +-
    > arch/powerpc/mm/mem.c | 2 +-
    > arch/s390/mm/init.c | 2 +-
    > arch/sh/mm/init.c | 2 +-
    > arch/x86/mm/init_32.c | 2 +-
    > arch/x86/mm/init_64.c | 2 +-
    > drivers/base/memory.c | 23 +++++++++--------------
    > include/linux/memory_hotplug.h | 2 +-
    > mm/memory_hotplug.c | 9 ++++++---
    > 9 files changed, 22 insertions(+), 24 deletions(-)
    >
    > diff --git a/arch/ia64/mm/init.c b/arch/ia64/mm/init.c
    > index 8f3efa682ee8..39e2aeb4669d 100644
    > --- a/arch/ia64/mm/init.c
    > +++ b/arch/ia64/mm/init.c
    > @@ -658,7 +658,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
    >
    > zone = pgdat->node_zones +
    > zone_for_memory(nid, start, size, ZONE_NORMAL, for_device);
    > - ret = __add_pages(nid, zone, start_pfn, nr_pages);
    > + ret = __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
    >
    > if (ret)
    > printk("%s: Problem encountered in __add_pages() as ret=%d\n",
    > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
    > index 9ee536ec0739..e6b2e6618b6c 100644
    > --- a/arch/powerpc/mm/mem.c
    > +++ b/arch/powerpc/mm/mem.c
    > @@ -151,7 +151,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
    > zone = pgdata->node_zones +
    > zone_for_memory(nid, start, size, 0, for_device);
    >
    > - return __add_pages(nid, zone, start_pfn, nr_pages);
    > + return __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
    > }
    >
    > #ifdef CONFIG_MEMORY_HOTREMOVE
    > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
    > index ee6a1d3d4983..893cf88cf02d 100644
    > --- a/arch/s390/mm/init.c
    > +++ b/arch/s390/mm/init.c
    > @@ -191,7 +191,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
    > continue;
    > nr_pages = (start_pfn + size_pages > zone_end_pfn) ?
    > zone_end_pfn - start_pfn : size_pages;
    > - rc = __add_pages(nid, zone, start_pfn, nr_pages);
    > + rc = __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
    > if (rc)
    > break;
    > start_pfn += nr_pages;
    > diff --git a/arch/sh/mm/init.c b/arch/sh/mm/init.c
    > index 75491862d900..a9d57f75ae8c 100644
    > --- a/arch/sh/mm/init.c
    > +++ b/arch/sh/mm/init.c
    > @@ -498,7 +498,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
    > ret = __add_pages(nid, pgdat->node_zones +
    > zone_for_memory(nid, start, size, ZONE_NORMAL,
    > for_device),
    > - start_pfn, nr_pages);
    > + start_pfn, nr_pages, !for_device);
    > if (unlikely(ret))
    > printk("%s: Failed, __add_pages() == %d\n", __func__, ret);
    >
    > diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
    > index 99fb83819a5f..94594b889144 100644
    > --- a/arch/x86/mm/init_32.c
    > +++ b/arch/x86/mm/init_32.c
    > @@ -831,7 +831,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
    > unsigned long start_pfn = start >> PAGE_SHIFT;
    > unsigned long nr_pages = size >> PAGE_SHIFT;
    >
    > - return __add_pages(nid, zone, start_pfn, nr_pages);
    > + return __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
    > }
    >
    > #ifdef CONFIG_MEMORY_HOTREMOVE
    > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
    > index 41270b96403d..2e004364a373 100644
    > --- a/arch/x86/mm/init_64.c
    > +++ b/arch/x86/mm/init_64.c
    > @@ -697,7 +697,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
    >
    > init_memory_mapping(start, start + size);
    >
    > - ret = __add_pages(nid, zone, start_pfn, nr_pages);
    > + ret = __add_pages(nid, zone, start_pfn, nr_pages, !for_device);
    > WARN_ON_ONCE(ret);
    >
    > /* update max_pfn, max_low_pfn and high_memory */
    > diff --git a/drivers/base/memory.c b/drivers/base/memory.c
    > index 90225ffee501..f8fd562c3f18 100644
    > --- a/drivers/base/memory.c
    > +++ b/drivers/base/memory.c
    > @@ -685,14 +685,6 @@ static int add_memory_block(int base_section_nr)
    > return 0;
    > }
    >
    > -static bool is_zone_device_section(struct mem_section *ms)
    > -{
    > - struct page *page;
    > -
    > - page = sparse_decode_mem_map(ms->section_mem_map, __section_nr(ms));
    > - return is_zone_device_page(page);
    > -}
    > -
    > /*
    > * need an interface for the VM to add new memory regions,
    > * but without onlining it.
    > @@ -702,9 +694,6 @@ int register_new_memory(int nid, struct mem_section *section)
    > int ret = 0;
    > struct memory_block *mem;
    >
    > - if (is_zone_device_section(section))
    > - return 0;
    > -
    > mutex_lock(&mem_sysfs_mutex);
    >
    > mem = find_memory_block(section);
    > @@ -741,11 +730,16 @@ static int remove_memory_section(unsigned long node_id,
    > {
    > struct memory_block *mem;
    >
    > - if (is_zone_device_section(section))
    > - return 0;
    > -
    > mutex_lock(&mem_sysfs_mutex);
    > +
    > + /*
    > + * Some users of the memory hotplug do not want/need memblock to
    > + * track all sections. Skip over those.
    > + */
    > mem = find_memory_block(section);
    > + if (!mem)
    > + goto out_unlock;
    > +
    > unregister_mem_sect_under_nodes(mem, __section_nr(section));
    >
    > mem->section_count--;
    > @@ -754,6 +748,7 @@ static int remove_memory_section(unsigned long node_id,
    > else
    > put_device(&mem->dev);
    >
    > +out_unlock:
    > mutex_unlock(&mem_sysfs_mutex);
    > return 0;
    > }
    > diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
    > index 134a2f69c21a..3c8cf86201c3 100644
    > --- a/include/linux/memory_hotplug.h
    > +++ b/include/linux/memory_hotplug.h
    > @@ -111,7 +111,7 @@ extern int __remove_pages(struct zone *zone, unsigned long start_pfn,
    >
    > /* reasonably generic interface to expand the physical pages in a zone */
    > extern int __add_pages(int nid, struct zone *zone, unsigned long start_pfn,
    > - unsigned long nr_pages);
    > + unsigned long nr_pages, bool want_memblock);
    >
    > #ifdef CONFIG_NUMA
    > extern int memory_add_physaddr_to_nid(u64 start);
    > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
    > index 6290d34b6331..a95120c56a9a 100644
    > --- a/mm/memory_hotplug.c
    > +++ b/mm/memory_hotplug.c
    > @@ -494,7 +494,7 @@ static int __meminit __add_zone(struct zone *zone, unsigned long phys_start_pfn)
    > }
    >
    > static int __meminit __add_section(int nid, struct zone *zone,
    > - unsigned long phys_start_pfn)
    > + unsigned long phys_start_pfn, bool want_memblock)
    > {
    > int ret;
    >
    > @@ -511,6 +511,9 @@ static int __meminit __add_section(int nid, struct zone *zone,
    > if (ret < 0)
    > return ret;
    >
    > + if (!want_memblock)
    > + return 0;
    > +
    > return register_new_memory(nid, __pfn_to_section(phys_start_pfn));
    > }
    >
    > @@ -521,7 +524,7 @@ static int __meminit __add_section(int nid, struct zone *zone,
    > * add the new pages.
    > */
    > int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
    > - unsigned long nr_pages)
    > + unsigned long nr_pages, bool want_memblock)
    > {
    > unsigned long i;
    > int err = 0;
    > @@ -549,7 +552,7 @@ int __ref __add_pages(int nid, struct zone *zone, unsigned long phys_start_pfn,
    > }
    >
    > for (i = start_sec; i <= end_sec; i++) {
    > - err = __add_section(nid, zone, section_nr_to_pfn(i));
    > + err = __add_section(nid, zone, section_nr_to_pfn(i), want_memblock);
    >
    > /*
    > * EEXIST is finally dealt with by ioresource collision
    > --
    > 2.11.0
    >

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