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

> >
> > /* 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
>

--
Sincerely yours,
Mike.

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