On 2020-09-30 17:30, Anshuman Khandual wrote:
On 10/01/2020 04:43 AM, Sudarshan Rajagopalan wrote:
When section mappings are enabled, we allocate vmemmap pages from
physically
continuous memory of size PMD_SIZE using vmemmap_alloc_block_buf().
Section
mappings are good to reduce TLB pressure. But when system is highly
fragmented
and memory blocks are being hot-added at runtime, its possible that
such
physically continuous memory allocations can fail. Rather than failing
the
memory hot-add procedure, add a fallback option to allocate vmemmap
pages from
discontinuous pages using vmemmap_populate_basepages().
Signed-off-by: Sudarshan Rajagopalan <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Anshuman Khandual <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Logan Gunthorpe <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Steven Price <[email protected]>
---
arch/arm64/mm/mmu.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 75df62f..9edbbb8 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1121,8 +1121,18 @@ int __meminit vmemmap_populate(unsigned long
start, unsigned long end, int node,
void *p = NULL;
p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
- if (!p)
- return -ENOMEM;
+ if (!p) {
+ if (altmap)
+ return -ENOMEM; /* no fallback */
Why ? If huge pages inside a vmemmap section might have been allocated
from altmap, the base page could also fallback on altmap. If this patch
has just followed the existing x86 semantics, it was written [1] long
back before vmemmap_populate_basepages() supported altmap allocation.
While adding that support [2] recently, it was deliberate not to change
x86 semantics as it was a platform decision. Nonetheless, it makes
sense
to fallback on altmap bases pages if and when required.
[1] 4b94ffdc4163 (x86, mm: introduce vmem_altmap to augment
vmemmap_populate())
[2] 1d9cfee7535c (mm/sparsemem: enable vmem_altmap support in
vmemmap_populate_basepages())
Yes agreed. We can allow fallback on altmap as well. I did indeed follow
x86 semantics. Will send the updated patch.
Sudarshan
--
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