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

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