[PATCH 4/6] powerpc: Chunk calls to flush_dcache_range in arch_*_memory

[Alastair D'Silva]

From: Alastair D'Silva <alast...@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 16GB chunks, calling
cond_resched() inbetween to allow the scheduler to run.

Signed-off-by: Alastair D'Silva <alast...@d-silva.org>
---
 arch/powerpc/mm/mem.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 5400da87a804..fb0d5e9aa11b 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 (16ull * 1024ull * 1024ull * 1024ull)
+
 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;
+       unsigned long i;
        int rc;
 
        resize_hpt_for_hotplug(memblock_phys_mem_size());
@@ -120,7 +123,11 @@ 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 +138,18 @@ 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);
+       unsigned long 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