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FAILED: patch "[PATCH] powerpc: Chunk calls to flush_dcache_range in arch_*_memory" failed to apply to 4.19-stable tree

PATCH [email protected] 1 participant 1 message Jan 7, 2020

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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 <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 076265907cf9633bbef861c7c2a1c26a8209f283 Mon Sep 17 00:00:00 2001
From: Alastair D'Silva <[email protected]>
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 <[email protected]>
Signed-off-by Michael Ellerman <[email protected]>
Link https://lore.kernel.org/r/[email protected] open here
arch/powerpc/mm/mem.c +25 -2
index 3392cacabe60..634e5ea55b6b 100644
@@ -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);