The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 076265907cf9633bbef861c7c2a1c26a8209f283 Mon Sep 17 00:00:00 2001
From: Alastair D'Silva alastair@d-silva.org Date: Mon, 4 Nov 2019 13:32:57 +1100 Subject: [PATCH] powerpc: Chunk calls to flush_dcache_range in arch_*_memory
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.
Fixes: fb5924fddf9e ("powerpc/mm: Flush cache on memory hot(un)plug") Signed-off-by: Alastair D'Silva alastair@d-silva.org Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20191104023305.9581-6-alastair@au1.ibm.com
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c index 3392cacabe60..634e5ea55b6b 100644 --- a/arch/powerpc/mm/mem.c +++ b/arch/powerpc/mm/mem.c @@ -104,6 +104,27 @@ int __weak remove_section_mapping(unsigned long start, unsigned long end) return -ENODEV; }
+#define FLUSH_CHUNK_SIZE SZ_1G +/** + * flush_dcache_range_chunked(): Write any modified data cache blocks out to + * memory and invalidate them, in chunks of up to FLUSH_CHUNK_SIZE + * Does not invalidate the corresponding instruction cache blocks. + * + * @start: the start address + * @stop: the stop address (exclusive) + * @chunk: the max size of the chunks + */ +static void flush_dcache_range_chunked(unsigned long start, unsigned long stop, + unsigned long chunk) +{ + unsigned long i; + + for (i = start; i < stop; i += chunk) { + flush_dcache_range(i, min(stop, start + chunk)); + cond_resched(); + } +} + int __ref arch_add_memory(int nid, u64 start, u64 size, struct mhp_restrictions *restrictions) { @@ -120,7 +141,8 @@ int __ref arch_add_memory(int nid, u64 start, u64 size, start, start + size, rc); return -EFAULT; } - flush_dcache_range(start, start + size); + + flush_dcache_range_chunked(start, start + size, FLUSH_CHUNK_SIZE);
return __add_pages(nid, start_pfn, nr_pages, restrictions); } @@ -137,7 +159,8 @@ void __ref arch_remove_memory(int nid, u64 start, u64 size,
/* Remove htab bolted mappings for this section of memory */ start = (unsigned long)__va(start); - flush_dcache_range(start, start + size); + flush_dcache_range_chunked(start, start + size, FLUSH_CHUNK_SIZE); + ret = remove_section_mapping(start, start + size); WARN_ON_ONCE(ret);