Will,
(+ Cc: Dennis)

On Thu, Nov 10, 2016 at 05:27:20PM +0000, Will Deacon wrote:

On Wed, Nov 02, 2016 at 01:51:53PM +0900, AKASHI Takahiro wrote:

quoted

Add memblock_cap_memory_range() which will remove all the memblock regions
except the range specified in the arguments.

This function, like memblock_mem_limit_remove_map(), will not remove
memblocks with MEMMAP_NOMAP attribute as they may be mapped and accessed
later as "device memory."
See the commit a571d4eb55d8 ("mm/memblock.c: add new infrastructure to
address the mem limit issue").

This function is used, in a succeeding patch in the series of arm64 kdump
suuport, to limit the range of usable memory, System RAM, on crash dump
kernel.
(Please note that "mem=" parameter is of little use for this purpose.)

Signed-off-by: AKASHI Takahiro <redacted>
Cc: linux-mm at kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 include/linux/memblock.h |  1 +
 mm/memblock.c            | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 5b759c9..0e770af 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h

@@ -334,6 +334,7 @@ phys_addr_t memblock_start_of_DRAM(void);
 phys_addr_t memblock_end_of_DRAM(void);
 void memblock_enforce_memory_limit(phys_addr_t memory_limit);
 void memblock_mem_limit_remove_map(phys_addr_t limit);
+void memblock_cap_memory_range(phys_addr_t base, phys_addr_t size);
 bool memblock_is_memory(phys_addr_t addr);
 int memblock_is_map_memory(phys_addr_t addr);
 int memblock_is_region_memory(phys_addr_t base, phys_addr_t size);

diff --git a/mm/memblock.c b/mm/memblock.c
index 7608bc3..eb53876 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c

@@ -1544,6 +1544,34 @@ void __init memblock_mem_limit_remove_map(phys_addr_t limit)
 			      (phys_addr_t)ULLONG_MAX);
 }
 
+void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
+{
+	int start_rgn, end_rgn;
+	int i, ret;
+
+	if (!size)
+		return;
+
+	ret = memblock_isolate_range(&memblock.memory, base, size,
+						&start_rgn, &end_rgn);
+	if (ret)
+		return;
+
+	/* remove all the MAP regions */
+	for (i = memblock.memory.cnt - 1; i >= end_rgn; i--)
+		if (!memblock_is_nomap(&memblock.memory.regions[i]))
+			memblock_remove_region(&memblock.memory, i);
+
+	for (i = start_rgn - 1; i >= 0; i--)
+		if (!memblock_is_nomap(&memblock.memory.regions[i]))
+			memblock_remove_region(&memblock.memory, i);
+
+	/* truncate the reserved regions */
+	memblock_remove_range(&memblock.reserved, 0, base);
+	memblock_remove_range(&memblock.reserved,
+			base + size, (phys_addr_t)ULLONG_MAX);
+}

This duplicates a bunch of the logic in memblock_mem_limit_remove_map. Can
you not implement that in terms of your new, more general, function? e.g.
by passing base == 0, and size == limit?

Obviously it's possible.
I actually talked to Dennis before about merging them,
but he was against my idea.

Thanks,
-Takahiro AKASHI

Will