From: George Guo The default percentage-based policy sizes scratch areas from the current kernel's MEMBLOCK_RSRV_KERN footprint. This is a reasonable heuristic for predicting the early memory demand of the next kernel. scratch_size_update() calculates the lowmem and global sizes before either area is allocated. However, kho_reserve_scratch() calculates each per-node size only after allocating the lowmem and global areas. Since memblock allocations are marked MEMBLOCK_RSRV_KERN, the per-node calculation includes those newly allocated scratch areas and scales them again. This feedback substantially inflates the per-node request. On a 1 GiB LoongArch QEMU guest, the relevant reservation baseline is about 98.45 MiB. With the default 200% scale and 32 MiB alignment, the old ordering allocates 224 MiB of lowmem scratch, then requests 672 MiB for node 0, for a total of 896 MiB. The node allocation fails and KHO is disabled. The same incorrect calculation is hidden on the tested 1 GiB x86 guest because its baseline is smaller and its memory map can satisfy the inflated request. Calculate and save all per-node sizes in the scratch descriptors before reserving any scratch areas, then use the saved sizes during allocation. This keeps the percentage heuristic while preventing scratch memory from becoming input to the sizing of more scratch memory. On the LoongArch guest, the aligned total is reduced from 896 MiB to 448 MiB. The KHO vmtest passes on 1 GiB LoongArch and x86 QEMU guests with this change. Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers") Reported-by: Kexin Liu Co-developed-by: Kexin Liu Signed-off-by: Kexin Liu Signed-off-by: George Guo --- kernel/liveupdate/kexec_handover.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c index 7c4d86daf86d..39f489a258d9 100644 --- a/kernel/liveupdate/kexec_handover.c +++ b/kernel/liveupdate/kexec_handover.c @@ -847,6 +847,17 @@ static void __init kho_reserve_scratch(void) goto err_disable_kho; } + /* + * Calculate the per-node sizes before reserving any scratch areas. + * memblock allocations are marked MEMBLOCK_RSRV_KERN, so calculating + * them later would count the lowmem and global scratch areas as kernel + * allocations and scale them again. + */ + i = 2; + for_each_node_state(nid, N_MEMORY) + kho_scratch[i++].size = scratch_size_node(nid); + i = 0; + /* * reserve scratch area in low memory for lowmem allocations in the * next kernel @@ -880,7 +891,7 @@ static void __init kho_reserve_scratch(void) * memoryless nodes, as we can not allocate scratch areas there. */ for_each_node_state(nid, N_MEMORY) { - size = scratch_size_node(nid); + size = kho_scratch[i].size; addr = memblock_alloc_range_nid(size, SCRATCH_ALIGNMENT_BYTES, 0, MEMBLOCK_ALLOC_ACCESSIBLE, nid, true); -- 2.53.0