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Subject[PATCH v2 4/6] powerpc: Chunk calls to flush_dcache_range in arch_*_memory
Date
From: Alastair D'Silva <alastair@d-silva.org>

When presented with large amounts of memory being hotplugged
(in my test case, ~890GB), the call to flush_dcache_range takes
a while (~50 seconds), triggering RCU stalls.

This patch breaks up the call into 1GB chunks, calling
cond_resched() inbetween to allow the scheduler to run.

Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
---
arch/powerpc/mm/mem.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index cd540123874d..854aaea2c6ae 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -104,11 +104,14 @@ int __weak remove_section_mapping(unsigned long start, unsigned long end)
return -ENODEV;
}

+#define FLUSH_CHUNK_SIZE SZ_1G
+
int __ref arch_add_memory(int nid, u64 start, u64 size,
struct mhp_restrictions *restrictions)
{
unsigned long start_pfn = start >> PAGE_SHIFT;
unsigned long nr_pages = size >> PAGE_SHIFT;
+ u64 i;
int rc;

resize_hpt_for_hotplug(memblock_phys_mem_size());
@@ -120,7 +123,12 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
start, start + size, rc);
return -EFAULT;
}
- flush_dcache_range(start, start + size);
+
+ for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {
+ flush_dcache_range(start + i,
+ min(start + size, start + i + FLUSH_CHUNK_SIZE));
+ cond_resched();
+ }

return __add_pages(nid, start_pfn, nr_pages, restrictions);
}
@@ -131,13 +139,19 @@ void __ref arch_remove_memory(int nid, u64 start, u64 size,
unsigned long start_pfn = start >> PAGE_SHIFT;
unsigned long nr_pages = size >> PAGE_SHIFT;
struct page *page = pfn_to_page(start_pfn) + vmem_altmap_offset(altmap);
+ u64 i;
int ret;

__remove_pages(page_zone(page), start_pfn, nr_pages, altmap);

/* Remove htab bolted mappings for this section of memory */
start = (unsigned long)__va(start);
- flush_dcache_range(start, start + size);
+ for (i = 0; i < size; i += FLUSH_CHUNK_SIZE) {
+ flush_dcache_range(start + i,
+ min(start + size, start + i + FLUSH_CHUNK_SIZE));
+ cond_resched();
+ }
+
ret = remove_section_mapping(start, start + size);
WARN_ON_ONCE(ret);

--
2.21.0
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