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Sashiko AI review found 1 potential issue(s) to consider: > - [High] kho: lowmem scratch exhaustion due to missing node-specific lowmem reservations > -- > > commit 45b67db1813edaa6fb1bdfe7033f0598a814cd63 > Author: Sourabh Jain > > kho: fix global scratch size calculation > > This commit updates the scratch size calculations to correctly distinguish > between memory reserved for a specific NUMA node and memory reserved with > NUMA_NO_NODE. It introduces memblock_reserved_size_nid() to calculate > reserved memory based on reservation type and NUMA node, fixing an issue > where per-node reservations were incorrectly included in the global scratch > allocation. > >> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c >> index 7c4d86daf86d5..dc809e1e768c0 100644 >> --- a/kernel/liveupdate/kexec_handover.c >> +++ b/kernel/liveupdate/kexec_handover.c > [ ... ] >> @@ -787,17 +787,17 @@ static void __init scratch_size_update(void) >> if (scratch_scale) { >> phys_addr_t size; >> >> - size = memblock_reserved_kern_size(ARCH_LOW_ADDRESS_LIMIT, >> - NUMA_NO_NODE); >> - size -= memblock_reserved_hugetlb_size(ARCH_LOW_ADDRESS_LIMIT, >> - NUMA_NO_NODE); >> + size = memblock_reserved_size_nid(ARCH_LOW_ADDRESS_LIMIT, NUMA_NO_NODE, >> + MEMBLOCK_RSRV_KERN); > [Severity: High] > Does checking NUMA_NO_NODE here exclude node-specific lowmem reservations > (like node-bound DMA pools) from the lowmem scratch size calculation? No. Node-specific reservations are handled separately. The node-specific scratch memory size is calculated in scratch_size_node(), so if the kernel has made a node-specific allocation, KHO will reserve scratch memory on the corresponding node. > If the successor kernel requires lowmem for these node-specific reservations > during early boot, could shrinking the global lowmem scratch memory lead to > memblock allocation failures and a panic? With this fix, KHO still reserves both per-node scratch memory and lowmem scratch memory to meet the needs of the successor kernel. Per-node scratch memory is reserved on the corresponding node. The only change is that per-node allocations made in lowmem (below 4G by-default) are no longer counted when calculating the lowmem scratch size. >> + size -= memblock_reserved_size_nid(ARCH_LOW_ADDRESS_LIMIT, NUMA_NO_NODE, >> + MEMBLOCK_RSRV_HUGETLB); >> size = size * scratch_scale / 100; >> scratch_size_lowmem = size; > [ ... ] >> @@ -815,11 +815,11 @@ static phys_addr_t __init scratch_size_node(int nid) >> phys_addr_t size; >> >> if (scratch_scale) { >> - size = memblock_reserved_kern_size(MEMBLOCK_ALLOC_ANYWHERE, >> - nid); >> + size = memblock_reserved_size_nid(MEMBLOCK_ALLOC_ANYWHERE, nid, >> + MEMBLOCK_RSRV_KERN); > [Severity: High] > Are the node-specific lowmem reservations that were excluded from > scratch_size_lowmem now being counted here instead? Since this counts > with MEMBLOCK_ALLOC_ANYWHERE, will these reservations potentially be satisfied > using scratch memory in highmem? No. > > If the successor kernel restricts its memblock allocations to > MEMBLOCK_KHO_SCRATCH regions, won't it be unable to recreate its > node-specific lowmem reservations if the per-node scratch memory was placed > in highmem? The per-node scratch memory will be allocated on the corresponding node. Therefore, the successor kernel should be able to recreate its node-specific reservations, even if the per-node scratch memory is placed in highmem. > >> /* Do not count HugeTLB pages. */ >> - size -= memblock_reserved_hugetlb_size(MEMBLOCK_ALLOC_ANYWHERE, >> - nid); >> + size -= memblock_reserved_size_nid(MEMBLOCK_ALLOC_ANYWHERE, nid, >> + MEMBLOCK_RSRV_HUGETLB); >> size = size * scratch_scale / 100; >> } else { >> size = scratch_size_pernode;