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SubjectRe: [PATCH v3 3/4] arm64: kdump: support more than one crash kernel regions
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Hi Mike,

On 2019/4/14 20:10, Mike Rapoport wrote:
> Hi,
>
> On Thu, Apr 11, 2019 at 08:17:43PM +0800, Chen Zhou wrote:
>> Hi Mike,
>>
>> This overall looks well.
>> Replacing memblock_cap_memory_range() with memblock_cap_memory_ranges() was what i wanted
>> to do in v1, sorry for don't express that clearly.
>
> I didn't object to memblock_cap_memory_ranges() in general, I was worried
> about it's complexity and I hoped that we could find a simpler solution.
>
>> But there are some issues as below. After fixing this, it can work correctly.
>>
>> On 2019/4/10 21:09, Mike Rapoport wrote:
>>> Hi,
>>>
>>> On Tue, Apr 09, 2019 at 06:28:18PM +0800, Chen Zhou wrote:
>>>> After commit (arm64: kdump: support reserving crashkernel above 4G),
>>>> there may be two crash kernel regions, one is below 4G, the other is
>>>> above 4G.
>>>>
>>>> Crash dump kernel reads more than one crash kernel regions via a dtb
>>>> property under node /chosen,
>>>> linux,usable-memory-range = <BASE1 SIZE1 [BASE2 SIZE2]>
>>>>
>>>> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
>>>> ---
>>>> arch/arm64/mm/init.c | 66 ++++++++++++++++++++++++++++++++++++++++--------
>>>> include/linux/memblock.h | 6 +++++
>>>> mm/memblock.c | 7 ++---
>>>> 3 files changed, 66 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>>> index 3bebddf..0f18665 100644
>>>> --- a/arch/arm64/mm/init.c
>>>> +++ b/arch/arm64/mm/init.c
>>>> @@ -65,6 +65,11 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>>>
>>>> #ifdef CONFIG_KEXEC_CORE
>>>>
>>>> +/* at most two crash kernel regions, low_region and high_region */
>>>> +#define CRASH_MAX_USABLE_RANGES 2
>>>> +#define LOW_REGION_IDX 0
>>>> +#define HIGH_REGION_IDX 1
>>>> +
>>>> /*
>>>> * reserve_crashkernel() - reserves memory for crash kernel
>>>> *
>>>> @@ -297,8 +302,8 @@ static int __init early_init_dt_scan_usablemem(unsigned long node,
>>>> const char *uname, int depth, void *data)
>>>> {
>>>> struct memblock_region *usablemem = data;
>>>> - const __be32 *reg;
>>>> - int len;
>>>> + const __be32 *reg, *endp;
>>>> + int len, nr = 0;
>>>>
>>>> if (depth != 1 || strcmp(uname, "chosen") != 0)
>>>> return 0;
>>>> @@ -307,22 +312,63 @@ static int __init early_init_dt_scan_usablemem(unsigned long node,
>>>> if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
>>>> return 1;
>>>>
>>>> - usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
>>>> - usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
>>>> + endp = reg + (len / sizeof(__be32));
>>>> + while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
>>>> + usablemem[nr].base = dt_mem_next_cell(dt_root_addr_cells, &reg);
>>>> + usablemem[nr].size = dt_mem_next_cell(dt_root_size_cells, &reg);
>>>> +
>>>> + if (++nr >= CRASH_MAX_USABLE_RANGES)
>>>> + break;
>>>> + }
>>>>
>>>> return 1;
>>>> }
>>>>
>>>> static void __init fdt_enforce_memory_region(void)
>>>> {
>>>> - struct memblock_region reg = {
>>>> - .size = 0,
>>>> - };
>>>> + int i, cnt = 0;
>>>> + struct memblock_region regs[CRASH_MAX_USABLE_RANGES];
>>>
>>> I only now noticed that fdt_enforce_memory_region() uses memblock_region to
>>> pass the ranges around. If we'd switch to memblock_type instead, the
>>> implementation of memblock_cap_memory_ranges() would be really
>>> straightforward. Can you check if the below patch works for you?
>>>
>>> >From e476d584098e31273af573e1a78e308880c5cf28 Mon Sep 17 00:00:00 2001
>>> From: Mike Rapoport <rppt@linux.ibm.com>
>>> Date: Wed, 10 Apr 2019 16:02:32 +0300
>>> Subject: [PATCH] memblock: extend memblock_cap_memory_range to multiple ranges
>>>
>>> The memblock_cap_memory_range() removes all the memory except the range
>>> passed to it. Extend this function to recieve memblock_type with the
>>> regions that should be kept. This allows switching to simple iteration over
>>> memblock arrays with 'for_each_mem_range' to remove the unneeded memory.
>>>
>>> Enable use of this function in arm64 for reservation of multile regions for
>>> the crash kernel.
>>>
>>> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
>>> ---
>>> arch/arm64/mm/init.c | 34 ++++++++++++++++++++++++----------
>>> include/linux/memblock.h | 2 +-
>>> mm/memblock.c | 45 ++++++++++++++++++++++-----------------------
>>> 3 files changed, 47 insertions(+), 34 deletions(-)
>>>
>>>
>>> -void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
>>> +void __init memblock_cap_memory_ranges(struct memblock_type *regions_to_keep)
>>> {
>>> - 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);
>>> + phys_addr_t start, end;
>>> + u64 i;
>>>
>>> - for (i = start_rgn - 1; i >= 0; i--)
>>> - if (!memblock_is_nomap(&memblock.memory.regions[i]))
>>> - memblock_remove_region(&memblock.memory, i);
>>> + /* truncate memory while skipping NOMAP regions */
>>> + for_each_mem_range(i, &memblock.memory, regions_to_keep, NUMA_NO_NODE,
>>> + MEMBLOCK_NONE, &start, &end, NULL)
>>> + memblock_remove(start, end);
>>
>> 1. use memblock_remove(start, size) instead of memblock_remove(start, end).
>>
>> 2. There is a another hidden issue. We couldn't mix __next_mem_range()(called by for_each_mem_range) operation
>> with remove operation because __next_mem_range() records the index of last time. If we do remove between
>> __next_mem_range(), the index may be mess.
>
> Oops, I've really missed that :)
>
>> Therefore, we could do remove operation after for_each_mem_range like this, solution A:
>> void __init memblock_cap_memory_ranges(struct memblock_type *regions_to_keep)
>> {
>> - phys_addr_t start, end;
>> - u64 i;
>> + phys_addr_t start[INIT_MEMBLOCK_RESERVED_REGIONS * 2];
>> + phys_addr_t end[INIT_MEMBLOCK_RESERVED_REGIONS * 2];
>> + u64 i, nr = 0;
>>
>> /* truncate memory while skipping NOMAP regions */
>> for_each_mem_range(i, &memblock.memory, regions_to_keep, NUMA_NO_NODE,
>> - MEMBLOCK_NONE, &start, &end, NULL)
>> - memblock_remove(start, end);
>> + MEMBLOCK_NONE, &start[nr], &end[nr], NULL)
>> + nr++;
>> + for (i = 0; i < nr; i++)
>> + memblock_remove(start[i], end[i] - start[i]);
>>
>> /* truncate the reserved regions */
>> + nr = 0;
>> for_each_mem_range(i, &memblock.reserved, regions_to_keep, NUMA_NO_NODE,
>> - MEMBLOCK_NONE, &start, &end, NULL)
>> - memblock_remove_range(&memblock.reserved, start, end);
>> + MEMBLOCK_NONE, &start[nr], &end[nr], NULL)
>> + nr++;
>> + for (i = 0; i < nr; i++)
>> + memblock_remove_range(&memblock.reserved, start[i],
>> + end[i] - start[i]);
>> }
>>
>> But a warning occurs when compiling:
>> CALL scripts/atomic/check-atomics.sh
>> CALL scripts/checksyscalls.sh
>> CHK include/generated/compile.h
>> CC mm/memblock.o
>> mm/memblock.c: In function ‘memblock_cap_memory_ranges’:
>> mm/memblock.c:1635:1: warning: the frame size of 36912 bytes is larger than 2048 bytes [-Wframe-larger-than=]
>> }
>>
>> another solution is my implementation in v1, solution B:
>> +void __init memblock_cap_memory_ranges(struct memblock_type *regions_to_keep)
>> +{
>> + int start_rgn[INIT_MEMBLOCK_REGIONS], end_rgn[INIT_MEMBLOCK_REGIONS];
>> + int i, j, ret, nr = 0;
>> + memblock_region *regs = regions_to_keep->regions;
>> +
>> + nr = regions_to_keep -> cnt;
>> + if (!nr)
>> + return;
>> +
>> + /* remove all the MAP regions */
>> + for (i = memblock.memory.cnt - 1; i >= end_rgn[nr - 1]; i--)
>> + if (!memblock_is_nomap(&memblock.memory.regions[i]))
>> + memblock_remove_region(&memblock.memory, i);
>> +
>> + for (i = nr - 1; i > 0; i--)
>> + for (j = start_rgn[i] - 1; j >= end_rgn[i - 1]; j--)
>> + if (!memblock_is_nomap(&memblock.memory.regions[j]))
>> + memblock_remove_region(&memblock.memory, j);
>> +
>> + for (i = start_rgn[0] - 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, regs[0].base);
>> +
>> + for (i = nr - 1; i > 0; i--)
>> + memblock_remove_range(&memblock.reserved,
>> + regs[i - 1].base + regs[i - 1].size,
>> + regs[i].base - regs[i - 1].base - regs[i - 1].size);
>> +
>> + memblock_remove_range(&memblock.reserved,
>> + regs[nr - 1].base + regs[nr - 1].size, PHYS_ADDR_MAX);
>> +}
>>
>> solution A: phys_addr_t start[INIT_MEMBLOCK_RESERVED_REGIONS * 2];
>> phys_addr_t end[INIT_MEMBLOCK_RESERVED_REGIONS * 2];
>> start, end is physical addr
>>
>> solution B: int start_rgn[INIT_MEMBLOCK_REGIONS], end_rgn[INIT_MEMBLOCK_REGIONS];
>> start_rgn, end_rgn is rgn index
>>
>> Solution B do less remove operations and with no warning comparing to solution A.
>> I think solution B is better, could you give some suggestions?
>
> Solution B is indeed better that solution A, but I'm still worried by
> relatively large arrays on stack and the amount of loops :(
>
> The very least we could do is to call memblock_cap_memory_range() to drop
> the memory before and after the ranges we'd like to keep.

1. relatively large arrays
As my said above, the start_rgn, end_rgn is rgn index, we could use unsigned char type.

2. loops
Loops always exist, and the solution with fewer loops may be just encapsulated well.

Thanks,
Chen Zhou

>
>>>
>>> /* truncate the reserved regions */
>>> - memblock_remove_range(&memblock.reserved, 0, base);
>>> - memblock_remove_range(&memblock.reserved,
>>> - base + size, PHYS_ADDR_MAX);
>>> + for_each_mem_range(i, &memblock.reserved, regions_to_keep, NUMA_NO_NODE,
>>> + MEMBLOCK_NONE, &start, &end, NULL)
>>> + memblock_remove_range(&memblock.reserved, start, end);
>>
>> There are the same issues as above.
>>
>>> }
>>>
>>> void __init memblock_mem_limit_remove_map(phys_addr_t limit)
>>> {
>>> + struct memblock_region rgn = {
>>> + .base = 0,
>>> + };
>>> +
>>> + struct memblock_type region_to_keep = {
>>> + .cnt = 1,
>>> + .max = 1,
>>> + .regions = &rgn,
>>> + };
>>> +
>>> phys_addr_t max_addr;
>>>
>>> if (!limit)
>>> @@ -1646,7 +1644,8 @@ void __init memblock_mem_limit_remove_map(phys_addr_t limit)
>>> if (max_addr == PHYS_ADDR_MAX)
>>> return;
>>>
>>> - memblock_cap_memory_range(0, max_addr);
>>> + region_to_keep.regions[0].size = max_addr;
>>> + memblock_cap_memory_ranges(&region_to_keep);
>>> }
>>>
>>> static int __init_memblock memblock_search(struct memblock_type *type, phys_addr_t addr)
>>>
>>
>> Thanks,
>> Chen Zhou
>>
>

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