On Wed, Feb 19, 2025 at 09:24:31AM +0200, Mike Rapoport wrote:
>Hi,
>
>On Tue, Feb 18, 2025 at 03:50:04PM +0000, Wei Yang wrote:
>> On Thu, Feb 06, 2025 at 03:27:42PM +0200, Mike Rapoport wrote:
>> >From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
>> >
>> >to denote areas that were reserved for kernel use either directly with
>> >memblock_reserve_kern() or via memblock allocations.
>> >
>> >Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
>> >---
>> > include/linux/memblock.h | 16 +++++++++++++++-
>> > mm/memblock.c | 32 ++++++++++++++++++++++++--------
>> > 2 files changed, 39 insertions(+), 9 deletions(-)
>> >
>> >diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> >index e79eb6ac516f..65e274550f5d 100644
>> >--- a/include/linux/memblock.h
>> >+++ b/include/linux/memblock.h
>> >@@ -50,6 +50,7 @@ enum memblock_flags {
>> > MEMBLOCK_NOMAP = 0x4, /* don't add to kernel direct mapping */
>> > MEMBLOCK_DRIVER_MANAGED = 0x8, /* always detected via a driver */
>> > MEMBLOCK_RSRV_NOINIT = 0x10, /* don't initialize struct pages */
>> >+ MEMBLOCK_RSRV_KERN = 0x20, /* memory reserved for kernel use */
>>
>> Above memblock_flags, there are comments on explaining those flags.
>>
>> Seems we miss it for MEMBLOCK_RSRV_KERN.
>
>Right, thanks!
>
>> >
>> > #ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
>> >@@ -1459,14 +1460,14 @@ phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
>> > again:
>> > found = memblock_find_in_range_node(size, align, start, end, nid,
>> > flags);
>> >- if (found && !memblock_reserve(found, size))
>> >+ if (found && !__memblock_reserve(found, size, nid, MEMBLOCK_RSRV_KERN))
>>
>> Maybe we could use memblock_reserve_kern() directly. If my understanding is
>> correct, the reserved region's nid is not used.
>
>We use nid of reserved regions in reserve_bootmem_region() (commit
>61167ad5fecd ("mm: pass nid to reserve_bootmem_region()")) but KHO needs to
>know the distribution of reserved memory among the nodes before
>memmap_init_reserved_pages().
>
>> BTW, one question here. How we handle concurrent memblock allocation? If two
>> threads find the same available range and do the reservation, it seems to be a
>> problem to me. Or I missed something?
>
>memblock allocations end before smp_init(), there is no possible concurrency.
>
Thanks, I still have one question here.
Below is a simplified call flow.
mm_core_init()
mem_init()
memblock_free_all()
free_low_memory_core_early()
memmap_init_reserved_pages()
memblock_set_node(..., memblock.reserved, ) --- (1)
__free_memory_core()
kmem_cache_init()
slab_state = UP; --- (2)
And memblock_allloc_range_nid() is not supposed to be called after
slab_is_available(). Even someone do dose it, it will get memory from slab
instead of reserve region in memblock.
