linux-kernel - [PATCH 6/6] powerpc: Don't flush caches when adding memory

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Date:   Thu, 15 Aug 2019 14:10:51 +1000
From:   "Alastair D'Silva" <alastair@....ibm.com>
To:     alastair@...ilva.org
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Qian Cai <cai@....pw>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Allison Randal <allison@...utok.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH 6/6] powerpc: Don't flush caches when adding memory

From: Alastair D'Silva <alastair@...ilva.org>

This operation takes a significant amount of time when hotplugging
large amounts of memory (~50 seconds with 890GB of persistent memory).

This was orignally in commit fb5924fddf9e
("powerpc/mm: Flush cache on memory hot(un)plug") to support memtrace,
but the flush on add is not needed as it is flushed on remove.

Signed-off-by: Alastair D'Silva <alastair@...ilva.org>
---
 arch/powerpc/mm/mem.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index fb0d5e9aa11b..43be99de7c9a 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -111,7 +111,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
 {
 	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());
@@ -124,11 +123,6 @@ int __ref arch_add_memory(int nid, u64 start, u64 size,
 		return -EFAULT;
 	}
 
-	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);
 }
 
-- 
2.21.0