Re: [PATCHv3 1/2] mm/memblock: extend the limit inferior of bottom-up after parsing hotplug attr

[Pingfan Liu <kernelfans@gmail.com>]

On Mon, Dec 31, 2018 at 4:40 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Fri, Dec 28, 2018 at 11:00:01AM +0800, Pingfan Liu wrote:
> > The bottom-up allocation style is introduced to cope with movable_node,
> > where the limit inferior of allocation starts from kernel's end, due to
> > lack of knowledge of memory hotplug info at this early time. But if later,
> > hotplug info has been got, the limit inferior can be extend to 0.
> > 'kexec -c' prefers to reuse this style to alloc mem at lower address,
> > since if the reserved region is beyond 4G, then it requires extra mem
> > (default is 16M) for swiotlb.
>
> I fail to understand why the availability of memory hotplug information
> would allow to extend the lower limit of bottom-up memblock allocations
> below the kernel. The memory in the physical range [0, kernel_start) can be
> allocated as soon as the kernel memory is reserved.
>
Yes, the  [0, kernel_start) can be allocated at this time by some func
e.g. memblock_reserve(). But there is trick. For the func like
memblock_find_in_range(), this is hotplug attr checking ,,it will
check the hotmovable attr in __next_mem_range()
{
if (movable_node_is_enabled() && memblock_is_hotpluggable(m))
continue
}.  So the movable memory can be safely skipped.

Thanks for your kindly review.

Regards,
Pingfan

> The extents of the memory node hosting the kernel image can be used to
> limit memblok allocations from that particular node, even in top-down mode.
>
> > Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> > Cc: Tang Chen <tangchen@cn.fujitsu.com>
> > Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> > Cc: Len Brown <lenb@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Jonathan Corbet <corbet@lwn.net>
> > Cc: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
> > Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
> > Cc: Nicholas Piggin <npiggin@gmail.com>
> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Cc: Daniel Vacek <neelx@redhat.com>
> > Cc: Mathieu Malaterre <malat@debian.org>
> > Cc: Stefan Agner <stefan@agner.ch>
> > Cc: Dave Young <dyoung@redhat.com>
> > Cc: Baoquan He <bhe@redhat.com>
> > Cc: yinghai@kernel.org,
> > Cc: vgoyal@redhat.com
> > Cc: linux-kernel@vger.kernel.org
> > ---
> >  drivers/acpi/numa.c      |  4 ++++
> >  include/linux/memblock.h |  1 +
> >  mm/memblock.c            | 58 +++++++++++++++++++++++++++++-------------------
> >  3 files changed, 40 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c
> > index 2746994..3eea4e4 100644
> > --- a/drivers/acpi/numa.c
> > +++ b/drivers/acpi/numa.c
> > @@ -462,6 +462,10 @@ int __init acpi_numa_init(void)
> >
> >               cnt = acpi_table_parse_srat(ACPI_SRAT_TYPE_MEMORY_AFFINITY,
> >                                           acpi_parse_memory_affinity, 0);
> > +
> > +#if defined(CONFIG_X86) || defined(CONFIG_ARM64)
> > +             mark_mem_hotplug_parsed();
> > +#endif
> >       }
> >
> >       /* SLIT: System Locality Information Table */
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index aee299a..d89ed9e 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -125,6 +125,7 @@ int memblock_reserve(phys_addr_t base, phys_addr_t size);
> >  void memblock_trim_memory(phys_addr_t align);
> >  bool memblock_overlaps_region(struct memblock_type *type,
> >                             phys_addr_t base, phys_addr_t size);
> > +void mark_mem_hotplug_parsed(void);
> >  int memblock_mark_hotplug(phys_addr_t base, phys_addr_t size);
> >  int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
> >  int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index 81ae63c..a3f5e46 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -231,6 +231,12 @@ __memblock_find_range_top_down(phys_addr_t start, phys_addr_t end,
> >       return 0;
> >  }
> >
> > +static bool mem_hotmovable_parsed __initdata_memblock;
> > +void __init_memblock mark_mem_hotplug_parsed(void)
> > +{
> > +     mem_hotmovable_parsed = true;
> > +}
> > +
> >  /**
> >   * memblock_find_in_range_node - find free area in given range and node
> >   * @size: size of free area to find
> > @@ -259,7 +265,7 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size,
> >                                       phys_addr_t end, int nid,
> >                                       enum memblock_flags flags)
> >  {
> > -     phys_addr_t kernel_end, ret;
> > +     phys_addr_t kernel_end, ret = 0;
> >
> >       /* pump up @end */
> >       if (end == MEMBLOCK_ALLOC_ACCESSIBLE)
> > @@ -270,34 +276,40 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t size,
> >       end = max(start, end);
> >       kernel_end = __pa_symbol(_end);
> >
> > -     /*
> > -      * try bottom-up allocation only when bottom-up mode
> > -      * is set and @end is above the kernel image.
> > -      */
> > -     if (memblock_bottom_up() && end > kernel_end) {
> > -             phys_addr_t bottom_up_start;
> > +     if (memblock_bottom_up()) {
> > +             phys_addr_t bottom_up_start = start;
> >
> > -             /* make sure we will allocate above the kernel */
> > -             bottom_up_start = max(start, kernel_end);
> > -
> > -             /* ok, try bottom-up allocation first */
> > -             ret = __memblock_find_range_bottom_up(bottom_up_start, end,
> > -                                                   size, align, nid, flags);
> > -             if (ret)
> > +             if (mem_hotmovable_parsed) {
> > +                     ret = __memblock_find_range_bottom_up(
> > +                             bottom_up_start, end, size, align, nid,
> > +                             flags);
> >                       return ret;
> >
> >               /*
> > -              * we always limit bottom-up allocation above the kernel,
> > -              * but top-down allocation doesn't have the limit, so
> > -              * retrying top-down allocation may succeed when bottom-up
> > -              * allocation failed.
> > -              *
> > -              * bottom-up allocation is expected to be fail very rarely,
> > -              * so we use WARN_ONCE() here to see the stack trace if
> > -              * fail happens.
> > +              * if mem hotplug info is not parsed yet, try bottom-up
> > +              * allocation with @end above the kernel image.
> >                */
> > -             WARN_ONCE(IS_ENABLED(CONFIG_MEMORY_HOTREMOVE),
> > +             } else if (!mem_hotmovable_parsed && end > kernel_end) {
> > +                     /* make sure we will allocate above the kernel */
> > +                     bottom_up_start = max(start, kernel_end);
> > +                     ret = __memblock_find_range_bottom_up(
> > +                             bottom_up_start, end, size, align, nid,
> > +                             flags);
> > +                     if (ret)
> > +                             return ret;
> > +                     /*
> > +                      * we always limit bottom-up allocation above the
> > +                      * kernel, but top-down allocation doesn't have
> > +                      * the limit, so retrying top-down allocation may
> > +                      * succeed when bottom-up allocation failed.
> > +                      *
> > +                      * bottom-up allocation is expected to be fail
> > +                      * very rarely, so we use WARN_ONCE() here to see
> > +                      * the stack trace if fail happens.
> > +                      */
> > +                     WARN_ONCE(IS_ENABLED(CONFIG_MEMORY_HOTREMOVE),
> >                         "memblock: bottom-up allocation failed, memory hotremove may be affected\n");
> > +             }
> >       }
> >
> >       return __memblock_find_range_top_down(start, end, size, align, nid,
> > --
> > 2.7.4
> >
>
> --
> Sincerely yours,
> Mike.
>