[PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Zhen Lei]

v2 --> v3:
1. Discard patch 3 in v2, a cleanup patch.

v1 --> v2:
1. Update the commit message of Patch 1, explicitly indicates that "crashkernel=X,high"
   is specified but "crashkernel=Y,low" is not specified.
2. Drop Patch 4-5. Currently, focus on function integrity, performance optimization
   will be considered in later versions.
3. Patch 3 is not mandatory, it's just a cleanup now, although it is a must for patch 4-5.
   But to avoid subsequent duplication of effort, I'm glad it was accepted.


v1:
After the basic functions of "support reserving crashkernel above 4G on arm64
kdump"(see https://lkml.org/lkml/2022/5/6/428) are implemented, we still have
three features to be improved.
1. When crashkernel=X,high is specified but crashkernel=Y,low is not specified,
   the default crash low memory size is provided.
2. For crashkernel=X without '@offset', if the low memory fails to be allocated,
   fall back to reserve region from high memory(above DMA zones).
3. If crashkernel=X,high is used, page mapping is performed only for the crash
   high memory, and block mapping is still used for other linear address spaces.
   Compared to the previous version:
   (1) For crashkernel=X[@offset], the memory above 4G is not changed to block
       mapping, leave it to the next time.
   (2) The implementation method is modified. Now the implementation is simpler
       and clearer.

Zhen Lei (2):
  arm64: kdump: Provide default size when crashkernel=Y,low is not
    specified
  arm64: kdump: Support crashkernel=X fall back to reserve region above
    DMA zones

 .../admin-guide/kernel-parameters.txt         | 10 ++-----
 arch/arm64/mm/init.c                          | 28 +++++++++++++++++--
 2 files changed, 28 insertions(+), 10 deletions(-)

-- 
2.25.1

[PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Zhen Lei]

To be consistent with the implementation of x86 and improve cross-platform
user experience. Try to allocate at least 256 MiB low memory automatically
for the case that crashkernel=,high is explicitly specified, while
crashkenrel=,low is omitted.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  8 +-------
 arch/arm64/mm/init.c                            | 12 +++++++++++-
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2522b11e593f239..65a2c3a22a4b57d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -843,7 +843,7 @@
 			available.
 			It will be ignored if crashkernel=X is specified.
 	crashkernel=size[KMG],low
-			[KNL, X86-64] range under 4G. When crashkernel=X,high
+			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
 			is passed, kernel could allocate physical memory region
 			above 4G, that cause second kernel crash on system
 			that require some amount of low memory, e.g. swiotlb
@@ -857,12 +857,6 @@
 			It will be ignored when crashkernel=X,high is not used
 			or memory reserved is below 4G.
 
-			[KNL, ARM64] range in low memory.
-			This one lets the user specify a low range in the
-			DMA zone for the crash dump kernel.
-			It will be ignored when crashkernel=X,high is not used
-			or memory reserved is located in the DMA zones.
-
 	cryptomgr.notests
 			[KNL] Disable crypto self-tests
 
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 339ee84e5a61a0b..5390f361208ccf7 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
 #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
 #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
 
+/*
+ * This is an empirical value in x86_64 and taken here directly. Please
+ * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
+ * details.
+ */
+#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
+	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
+
 static int __init reserve_crashkernel_low(unsigned long long low_size)
 {
 	unsigned long long low_base;
@@ -147,7 +155,9 @@ static void __init reserve_crashkernel(void)
 		 * is not allowed.
 		 */
 		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
-		if (ret && (ret != -ENOENT))
+		if (ret == -ENOENT)
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+		else if (ret)
 			return;
 
 		crash_max = CRASH_ADDR_HIGH_MAX;
-- 
2.25.1

[PATCH v3 2/2] arm64: kdump: Support crashkernel=X fall back to reserve region above DMA zones

[Zhen Lei]

For crashkernel=X without '@offset', select a region within DMA zones
first, and fall back to reserve region above DMA zones. This allows
users to use the same configuration on multiple platforms.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  2 +-
 arch/arm64/mm/init.c                            | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 65a2c3a22a4b57d..cb6a346419a1fe0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -823,7 +823,7 @@
 			memory region [offset, offset + size] for that kernel
 			image. If '@offset' is omitted, then a suitable offset
 			is selected automatically.
-			[KNL, X86-64] Select a region under 4G first, and
+			[KNL, X86-64, ARM64] Select a region under 4G first, and
 			fall back to reserve region above 4G when '@offset'
 			hasn't been specified.
 			See Documentation/admin-guide/kdump/kdump.rst for further details.
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 5390f361208ccf7..8539598f9e58b4d 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -138,6 +138,7 @@ static void __init reserve_crashkernel(void)
 	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
 	char *cmdline = boot_command_line;
 	int ret;
+	bool fixed_base;
 
 	if (!IS_ENABLED(CONFIG_KEXEC_CORE))
 		return;
@@ -166,15 +167,28 @@ static void __init reserve_crashkernel(void)
 		return;
 	}
 
+	fixed_base = !!crash_base;
 	crash_size = PAGE_ALIGN(crash_size);
 
 	/* User specifies base address explicitly. */
-	if (crash_base)
+	if (fixed_base)
 		crash_max = crash_base + crash_size;
 
+retry:
 	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
 					       crash_base, crash_max);
 	if (!crash_base) {
+		/*
+		 * Attempt to fully allocate low memory failed, fall back
+		 * to high memory, the minimum required low memory will be
+		 * reserved later.
+		 */
+		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
+			crash_max = CRASH_ADDR_HIGH_MAX;
+			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
+			goto retry;
+		}
+
 		pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
 			crash_size);
 		return;
-- 
2.25.1

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Baoquan He]

Hi Catalin,

On 07/11/22 at 05:03pm, Zhen Lei wrote:
> v2 --> v3:
> 1. Discard patch 3 in v2, a cleanup patch.
> 
> v1 --> v2:
> 1. Update the commit message of Patch 1, explicitly indicates that "crashkernel=X,high"
>    is specified but "crashkernel=Y,low" is not specified.
> 2. Drop Patch 4-5. Currently, focus on function integrity, performance optimization
>    will be considered in later versions.
> 3. Patch 3 is not mandatory, it's just a cleanup now, although it is a must for patch 4-5.
>    But to avoid subsequent duplication of effort, I'm glad it was accepted.
> 
> 
> v1:
> After the basic functions of "support reserving crashkernel above 4G on arm64
> kdump"(see https://lkml.org/lkml/2022/5/6/428) are implemented, we still have
> three features to be improved.
> 1. When crashkernel=X,high is specified but crashkernel=Y,low is not specified,
>    the default crash low memory size is provided.
> 2. For crashkernel=X without '@offset', if the low memory fails to be allocated,
>    fall back to reserve region from high memory(above DMA zones).
> 3. If crashkernel=X,high is used, page mapping is performed only for the crash
>    high memory, and block mapping is still used for other linear address spaces.
>    Compared to the previous version:
>    (1) For crashkernel=X[@offset], the memory above 4G is not changed to block
>        mapping, leave it to the next time.
>    (2) The implementation method is modified. Now the implementation is simpler
>        and clearer.

Do you have plan to pick this series so that it can be taken into 5.20
rc-1~3?

We have back ported the basic crashkernel=high, low, support into our
distros and have taken wide testing on arm64 servers, need this patchset
to back port for more testing. 

Thanks
Baoquan

> 
> Zhen Lei (2):
>   arm64: kdump: Provide default size when crashkernel=Y,low is not
>     specified
>   arm64: kdump: Support crashkernel=X fall back to reserve region above
>     DMA zones
> 
>  .../admin-guide/kernel-parameters.txt         | 10 ++-----
>  arch/arm64/mm/init.c                          | 28 +++++++++++++++++--
>  2 files changed, 28 insertions(+), 10 deletions(-)
> 
> -- 
> 2.25.1
> 

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Leizhen (ThunderTown)]

On 2022/8/1 16:20, Baoquan He wrote:
> Hi Catalin,
> 
> On 07/11/22 at 05:03pm, Zhen Lei wrote:
>> v2 --> v3:
>> 1. Discard patch 3 in v2, a cleanup patch.
>>
>> v1 --> v2:
>> 1. Update the commit message of Patch 1, explicitly indicates that "crashkernel=X,high"
>>    is specified but "crashkernel=Y,low" is not specified.
>> 2. Drop Patch 4-5. Currently, focus on function integrity, performance optimization
>>    will be considered in later versions.
>> 3. Patch 3 is not mandatory, it's just a cleanup now, although it is a must for patch 4-5.
>>    But to avoid subsequent duplication of effort, I'm glad it was accepted.
>>
>>
>> v1:
>> After the basic functions of "support reserving crashkernel above 4G on arm64
>> kdump"(see https://lkml.org/lkml/2022/5/6/428) are implemented, we still have
>> three features to be improved.
>> 1. When crashkernel=X,high is specified but crashkernel=Y,low is not specified,
>>    the default crash low memory size is provided.
>> 2. For crashkernel=X without '@offset', if the low memory fails to be allocated,
>>    fall back to reserve region from high memory(above DMA zones).
>> 3. If crashkernel=X,high is used, page mapping is performed only for the crash
>>    high memory, and block mapping is still used for other linear address spaces.
>>    Compared to the previous version:
>>    (1) For crashkernel=X[@offset], the memory above 4G is not changed to block
>>        mapping, leave it to the next time.
>>    (2) The implementation method is modified. Now the implementation is simpler
>>        and clearer.
> 
> Do you have plan to pick this series so that it can be taken into 5.20
> rc-1~3?

Hi, Catalin:
  Only function reserve_crashkernel() is modified in these two patches. The core
process of the arm64 architecture is not affected. I remember you suggested that
arm64 and x86 share the same kdump code, so these two subfeatures are needed.
Maybe we can lay the foundation first for the people who build the road. Unifying
the external interfaces of kdump on arm64 and x86 does not seem to hurt.


> 
> We have back ported the basic crashkernel=high, low, support into our
> distros and have taken wide testing on arm64 servers, need this patchset
> to back port for more testing. 
> 
> Thanks
> Baoquan
> 
>>
>> Zhen Lei (2):
>>   arm64: kdump: Provide default size when crashkernel=Y,low is not
>>     specified
>>   arm64: kdump: Support crashkernel=X fall back to reserve region above
>>     DMA zones
>>
>>  .../admin-guide/kernel-parameters.txt         | 10 ++-----
>>  arch/arm64/mm/init.c                          | 28 +++++++++++++++++--
>>  2 files changed, 28 insertions(+), 10 deletions(-)
>>
>> -- 
>> 2.25.1
>>
> 
> .
> 

-- 
Regards,
  Zhen Lei

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Will Deacon]

On Mon, Jul 11, 2022 at 05:03:18PM +0800, Zhen Lei wrote:
> To be consistent with the implementation of x86 and improve cross-platform
> user experience. Try to allocate at least 256 MiB low memory automatically
> for the case that crashkernel=,high is explicitly specified, while
> crashkenrel=,low is omitted.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
> Acked-by: Baoquan He <bhe@redhat.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  8 +-------
>  arch/arm64/mm/init.c                            | 12 +++++++++++-
>  2 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 2522b11e593f239..65a2c3a22a4b57d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -843,7 +843,7 @@
>  			available.
>  			It will be ignored if crashkernel=X is specified.
>  	crashkernel=size[KMG],low
> -			[KNL, X86-64] range under 4G. When crashkernel=X,high
> +			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
>  			is passed, kernel could allocate physical memory region
>  			above 4G, that cause second kernel crash on system
>  			that require some amount of low memory, e.g. swiotlb
> @@ -857,12 +857,6 @@
>  			It will be ignored when crashkernel=X,high is not used
>  			or memory reserved is below 4G.
>  
> -			[KNL, ARM64] range in low memory.
> -			This one lets the user specify a low range in the
> -			DMA zone for the crash dump kernel.
> -			It will be ignored when crashkernel=X,high is not used
> -			or memory reserved is located in the DMA zones.
> -
>  	cryptomgr.notests
>  			[KNL] Disable crypto self-tests
>  
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 339ee84e5a61a0b..5390f361208ccf7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>  
> +/*
> + * This is an empirical value in x86_64 and taken here directly. Please
> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
> + * details.

Honestly, I read that comment and I'm none the wiser. What does "due to
mapping restrictions" mean? The remainder of the comment appears to be
specific to x86 and refers to jump ranges with 5-level page-tables.

> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)

So why does this value make sense for arm64? We have considerable platform
fragmentation^Wdiversity compared to x86 and picking a one-size-fits-all
default is more likely to cause weird problems when it doesn't work imo. I'd
actually prefer that the default is something that fails obviously (e.g. 0)
and we force an appropriate size to be specified.

On the other hand, if you can convince me that having a global constant is
the right way forward, then please move this out of the arch code.

Will

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Leizhen (ThunderTown)]

On 2022/8/2 16:37, Will Deacon wrote:
> On Mon, Jul 11, 2022 at 05:03:18PM +0800, Zhen Lei wrote:
>> To be consistent with the implementation of x86 and improve cross-platform
>> user experience. Try to allocate at least 256 MiB low memory automatically
>> for the case that crashkernel=,high is explicitly specified, while
>> crashkenrel=,low is omitted.
>>
>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>> Acked-by: Baoquan He <bhe@redhat.com>
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt |  8 +-------
>>  arch/arm64/mm/init.c                            | 12 +++++++++++-
>>  2 files changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 2522b11e593f239..65a2c3a22a4b57d 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -843,7 +843,7 @@
>>  			available.
>>  			It will be ignored if crashkernel=X is specified.
>>  	crashkernel=size[KMG],low
>> -			[KNL, X86-64] range under 4G. When crashkernel=X,high
>> +			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
>>  			is passed, kernel could allocate physical memory region
>>  			above 4G, that cause second kernel crash on system
>>  			that require some amount of low memory, e.g. swiotlb
>> @@ -857,12 +857,6 @@
>>  			It will be ignored when crashkernel=X,high is not used
>>  			or memory reserved is below 4G.
>>  
>> -			[KNL, ARM64] range in low memory.
>> -			This one lets the user specify a low range in the
>> -			DMA zone for the crash dump kernel.
>> -			It will be ignored when crashkernel=X,high is not used
>> -			or memory reserved is located in the DMA zones.
>> -
>>  	cryptomgr.notests
>>  			[KNL] Disable crypto self-tests
>>  
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 339ee84e5a61a0b..5390f361208ccf7 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>>  
>> +/*
>> + * This is an empirical value in x86_64 and taken here directly. Please
>> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
>> + * details.
> 
> Honestly, I read that comment and I'm none the wiser. What does "due to
> mapping restrictions" mean? The remainder of the comment appears to be

Because the comments you read is addressed to CRASH_ADDR_LOW_MAX, not
for DEFAULT_CRASH_KERNEL_LOW_SIZE. Please see the following patch:

94fb9334182284 x86/crash: Allocate enough low memory when crashkernel=high

> specific to x86 and refers to jump ranges with 5-level page-tables.
> 
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
>> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
> 
> So why does this value make sense for arm64? We have considerable platform
> fragmentation^Wdiversity compared to x86 and picking a one-size-fits-all
> default is more likely to cause weird problems when it doesn't work imo. I'd
> actually prefer that the default is something that fails obviously (e.g. 0)
> and we force an appropriate size to be specified.
> 
> On the other hand, if you can convince me that having a global constant is
> the right way forward, then please move this out of the arch code.

Yes, the default value may not be the same as that of x86. For example,
128 MB may be sufficient.

So we need to discuss first, do we need a default value? Personally, I
don't think it hurts.

> 
> Will
> .
> 

-- 
Regards,
  Zhen Lei

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Baoquan He]

On 08/02/22 at 06:12pm, Leizhen (ThunderTown) wrote:
......snip...  
> >> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> >> index 339ee84e5a61a0b..5390f361208ccf7 100644
> >> --- a/arch/arm64/mm/init.c
> >> +++ b/arch/arm64/mm/init.c
> >> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
> >>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
> >>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
> >>  
> >> +/*
> >> + * This is an empirical value in x86_64 and taken here directly. Please
> >> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
> >> + * details.
> > 
> > Honestly, I read that comment and I'm none the wiser. What does "due to
> > mapping restrictions" mean? The remainder of the comment appears to be
> 
> Because the comments you read is addressed to CRASH_ADDR_LOW_MAX, not
> for DEFAULT_CRASH_KERNEL_LOW_SIZE. Please see the following patch:
> 
> 94fb9334182284 x86/crash: Allocate enough low memory when crashkernel=high
> 
> > specific to x86 and refers to jump ranges with 5-level page-tables.
> > 
> >> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
> >> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
> > 
> > So why does this value make sense for arm64? We have considerable platform
> > fragmentation^Wdiversity compared to x86 and picking a one-size-fits-all
> > default is more likely to cause weird problems when it doesn't work imo. I'd
> > actually prefer that the default is something that fails obviously (e.g. 0)
> > and we force an appropriate size to be specified.

The default value mainly serves the crashkernel=xM case, not just for
crashkernel=,high specified while no crahskernel=,low. The simplest
usage of crashkernel reservation is user only need set crashkernel=xM in
cmdline, we will try to get available memory from low memory region
firstly, if failed, go above 4G to find again. If we finally get memory
from above 4G, then the default low memory is needed. E.g if
crashkernel=512M is set, and no sufficient memory under 4G. With it,
user don't need to know about crashkernel=,high or ,low, and even memory
has type of high, low, or dma stuff.

> > 
> > On the other hand, if you can convince me that having a global constant is
> > the right way forward, then please move this out of the arch code.
> 
> Yes, the default value may not be the same as that of x86. For example,
> 128 MB may be sufficient.
> 
> So we need to discuss first, do we need a default value? Personally, I
> don't think it hurts.

Yes, we can discuss. Welcome anyone to help provide information how we
should take care to make a small but enough value. In fact, on x86_64,
we didn't set the value at one time. It was set as 72M at the beginning,
later Joerg found it's not enough, we finally decided to make it as
256M. People who mind the wasting of 256M can use crashkernel=,high and
crashkernel=,low pair to specify the value exactly.

commit c729de8fcea3 ("x86, kdump: Set crashkernel_low automatically")
commit 94fb93341822 ("x86/crash: Allocate enough low memory when crashkernel=high")

Thanks
Baoquan

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[john.p.donnelly]

On 8/1/22 9:47 PM, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/8/1 16:20, Baoquan He wrote:
>> Hi Catalin,
>>
>> On 07/11/22 at 05:03pm, Zhen Lei wrote:
>>> v2 --> v3:
>>> 1. Discard patch 3 in v2, a cleanup patch.
>>>
>>> v1 --> v2:
>>> 1. Update the commit message of Patch 1, explicitly indicates that "crashkernel=X,high"
>>>     is specified but "crashkernel=Y,low" is not specified.
>>> 2. Drop Patch 4-5. Currently, focus on function integrity, performance optimization
>>>     will be considered in later versions.
>>> 3. Patch 3 is not mandatory, it's just a cleanup now, although it is a must for patch 4-5.
>>>     But to avoid subsequent duplication of effort, I'm glad it was accepted.
>>>
>>>
>>> v1:
>>> After the basic functions of "support reserving crashkernel above 4G on arm64
>>> kdump"(see https://urldefense.com/v3/__https://lkml.org/lkml/2022/5/6/428__;!!ACWV5N9M2RV99hQ!ORBFa4UAmMss_79nuwu1kpW3D-mTela240vFo0FXOuV9QpGWy7Fp2H81ZjLPOuaufAQC_XBFEFGjAqs5njfGS6Rd4dZLhaez$ ) are implemented, we still have
>>> three features to be improved.
>>> 1. When crashkernel=X,high is specified but crashkernel=Y,low is not specified,
>>>     the default crash low memory size is provided.
>>> 2. For crashkernel=X without '@offset', if the low memory fails to be allocated,
>>>     fall back to reserve region from high memory(above DMA zones).
>>> 3. If crashkernel=X,high is used, page mapping is performed only for the crash
>>>     high memory, and block mapping is still used for other linear address spaces.
>>>     Compared to the previous version:
>>>     (1) For crashkernel=X[@offset], the memory above 4G is not changed to block
>>>         mapping, leave it to the next time.
>>>     (2) The implementation method is modified. Now the implementation is simpler
>>>         and clearer.
>>
>> Do you have plan to pick this series so that it can be taken into 5.20
>> rc-1~3?
> 
> Hi, Catalin:
>    Only function reserve_crashkernel() is modified in these two patches. The core
> process of the arm64 architecture is not affected. I remember you suggested that
> arm64 and x86 share the same kdump code, so these two subfeatures are needed.
> Maybe we can lay the foundation first for the people who build the road. Unifying
> the external interfaces of kdump on arm64 and x86 does not seem to hurt.
> 
> 
>>
>> We have back ported the basic crashkernel=high, low, support into our
>> distros and have taken wide testing on arm64 servers, need this patchset
>> to back port for more testing.
>>
>> Thanks
>> Baoquan
>>
>>>
>>> Zhen Lei (2):
>>>    arm64: kdump: Provide default size when crashkernel=Y,low is not
>>>      specified
>>>    arm64: kdump: Support crashkernel=X fall back to reserve region above
>>>      DMA zones
>>>
>>>   .../admin-guide/kernel-parameters.txt         | 10 ++-----
>>>   arch/arm64/mm/init.c                          | 28 +++++++++++++++++--
>>>   2 files changed, 28 insertions(+), 10 deletions(-)
>>>
>>> -- 
>>> 2.25.1
>>>
>>
>> .
>>
> 
Hi ,

What is the progress of this series ?

Without this patch set we are seeing  larger crashkernel=896M failures 
on Arm  with Linux-6.0.rc7.  This larger value is needed for
iSCSI booted systems with certain network adapters.


Thank you,
John.

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Baoquan He]

On 10/06/22 at 09:55am, john.p.donnelly@oracle.com wrote:
> On 8/1/22 9:47 PM, Leizhen (ThunderTown) wrote:
......
> > > Do you have plan to pick this series so that it can be taken into 5.20
> > > rc-1~3?
> > 
> > Hi, Catalin:
> >    Only function reserve_crashkernel() is modified in these two patches. The core
> > process of the arm64 architecture is not affected. I remember you suggested that
> > arm64 and x86 share the same kdump code, so these two subfeatures are needed.
> > Maybe we can lay the foundation first for the people who build the road. Unifying
> > the external interfaces of kdump on arm64 and x86 does not seem to hurt.
> > 
> > 
> > > 
> > > We have back ported the basic crashkernel=high, low, support into our
> > > distros and have taken wide testing on arm64 servers, need this patchset
> > > to back port for more testing.
> > > 
> > 
> Hi ,
> 
> What is the progress of this series ?
> 
> Without this patch set we are seeing  larger crashkernel=896M failures on
> Arm  with Linux-6.0.rc7.  This larger value is needed for
> iSCSI booted systems with certain network adapters.

This change is located in arch/arm64 folder, I have pinged arm64
maintainer to consider merging this patchset. Not sure if they are
still thinking, or ignore this.

Hi Catalin, Will,

Ping again!

Do you have plan to accept this patchset? It's very important for
crashkernel setting on arm64 with a simple and default syntax.

Thanks
Baoquan

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[John Donnelly]

On 10/13/22 05:46, Baoquan He wrote:
> On 10/06/22 at 09:55am, john.p.donnelly@oracle.com wrote:
>> On 8/1/22 9:47 PM, Leizhen (ThunderTown) wrote:
> ......
>>>> Do you have plan to pick this series so that it can be taken into 5.20
>>>> rc-1~3?
>>>
>>> Hi, Catalin:
>>>     Only function reserve_crashkernel() is modified in these two patches. The core
>>> process of the arm64 architecture is not affected. I remember you suggested that
>>> arm64 and x86 share the same kdump code, so these two subfeatures are needed.
>>> Maybe we can lay the foundation first for the people who build the road. Unifying
>>> the external interfaces of kdump on arm64 and x86 does not seem to hurt.
>>>
>>>
>>>>
>>>> We have back ported the basic crashkernel=high, low, support into our
>>>> distros and have taken wide testing on arm64 servers, need this patchset
>>>> to back port for more testing.
>>>>
>>>
>> Hi ,
>>
>> What is the progress of this series ?
>>
>> Without this patch set we are seeing  larger crashkernel=896M failures on
>> Arm  with Linux-6.0.rc7.  This larger value is needed for
>> iSCSI booted systems with certain network adapters.
> 
> This change is located in arch/arm64 folder, I have pinged arm64
> maintainer to consider merging this patchset. Not sure if they are
> still thinking, or ignore this.
> 
> Hi Catalin, Will,
> 
> Ping again!
> 
> Do you have plan to accept this patchset? It's very important fo
> crashkernel setting on arm64 with a simple and default syntax.
> 
> Thanks
> Baoquan
> 
Hi,

We have pulled this into our Linux 6.0.0 QA test kernels for now. We 
would like it added too.

Thank you,

John

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Catalin Marinas]

On Thu, Oct 13, 2022 at 06:46:35PM +0800, Baoquan He wrote:
> On 10/06/22 at 09:55am, john.p.donnelly@oracle.com wrote:
> > What is the progress of this series ?
> > 
> > Without this patch set we are seeing  larger crashkernel=896M failures on
> > Arm  with Linux-6.0.rc7.  This larger value is needed for
> > iSCSI booted systems with certain network adapters.
> 
> This change is located in arch/arm64 folder, I have pinged arm64
> maintainer to consider merging this patchset. Not sure if they are
> still thinking, or ignore this.
> 
> Hi Catalin, Will,
> 
> Ping again!
> 
> Do you have plan to accept this patchset? It's very important for
> crashkernel setting on arm64 with a simple and default syntax.

I'll look at it once the merging window closes. I saw discussions on
this thread and I ignored it until you all agreed ;).

-- 
Catalin

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[john.p.donnelly]

On 10/14/22 11:29 AM, Catalin Marinas wrote:
> On Thu, Oct 13, 2022 at 06:46:35PM +0800, Baoquan He wrote:
>> On 10/06/22 at 09:55am, john.p.donnelly@oracle.com wrote:
>>> What is the progress of this series ?
>>>
>>> Without this patch set we are seeing  larger crashkernel=896M failures on
>>> Arm  with Linux-6.0.rc7.  This larger value is needed for
>>> iSCSI booted systems with certain network adapters.
>>
>> This change is located in arch/arm64 folder, I have pinged arm64
>> maintainer to consider merging this patchset. Not sure if they are
>> still thinking, or ignore this.
>>
>> Hi Catalin, Will,
>>
>> Ping again!
>>
>> Do you have plan to accept this patchset? It's very important for
>> crashkernel setting on arm64 with a simple and default syntax.
> 
> I'll look at it once the merging window closes. I saw discussions on
> this thread and I ignored it until you all agreed ;).
> 


Hi,

Do you have a timeline for this ?  This crashkernel > 4G for Arm item 
has been lingering for 3 years. I think it is time for it to be 
incorporated.


Thanks,

John.

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Catalin Marinas]

On Mon, Jul 11, 2022 at 05:03:18PM +0800, Zhen Lei wrote:
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 339ee84e5a61a0b..5390f361208ccf7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>  
> +/*
> + * This is an empirical value in x86_64 and taken here directly. Please
> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
> + * details.
> + */
> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)

I agree with Will here, we need a better comment and we might as well
change the default value to something else until someone tells us that
the default is not large enough. The default swiotlb size is 64M, so we
need to cover that. The extra 8MB for any additional low allocations are
ok as well but the 256MB doesn't make much sense to me, or at least not
together with the rest.

If the main kernel got a command line option for a larger swiotlb, does
the crash kernel boot with the same command line? If not, we can just go
for a fixed 128M value here, which is double the default swiotlb buffer.

-- 
Catalin

Re: [PATCH v3 2/2] arm64: kdump: Support crashkernel=X fall back to reserve region above DMA zones

[Catalin Marinas]

On Mon, Jul 11, 2022 at 05:03:19PM +0800, Zhen Lei wrote:
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 5390f361208ccf7..8539598f9e58b4d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -138,6 +138,7 @@ static void __init reserve_crashkernel(void)
>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>  	char *cmdline = boot_command_line;
>  	int ret;
> +	bool fixed_base;
>  
>  	if (!IS_ENABLED(CONFIG_KEXEC_CORE))
>  		return;
> @@ -166,15 +167,28 @@ static void __init reserve_crashkernel(void)
>  		return;
>  	}
>  
> +	fixed_base = !!crash_base;
>  	crash_size = PAGE_ALIGN(crash_size);
>  
>  	/* User specifies base address explicitly. */
> -	if (crash_base)
> +	if (fixed_base)
>  		crash_max = crash_base + crash_size;

Not a fan of '!!', it is converted automatically. If you don't like the
conversion, just initialise fixed_base to false and here:

	if (crash_base) {
		fixed_base = true;
		crash_max = crash_base + crash_size;
	}

> +retry:
>  	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>  					       crash_base, crash_max);
>  	if (!crash_base) {
> +		/*
> +		 * Attempt to fully allocate low memory failed, fall back
> +		 * to high memory, the minimum required low memory will be
> +		 * reserved later.
> +		 */

I'm not sure this comment makes sense. If !crash_base, it doesn't mean
the kernel failed to fully allocate low memory. crash_max here could be
CRASH_ADDR_HIGH_MAX if crashkerne=X,high was specified. Maybe says
something like "If the first attempt was for low memory, fall back to
high ..."

> +		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
> +			crash_max = CRASH_ADDR_HIGH_MAX;
> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +			goto retry;
> +		}

The retry logic looks fine, it only happens once as crash_max is
updated.

-- 
Catalin

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Catalin Marinas]

On Mon, Jul 11, 2022 at 05:03:18PM +0800, Zhen Lei wrote:
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 2522b11e593f239..65a2c3a22a4b57d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -843,7 +843,7 @@
>  			available.
>  			It will be ignored if crashkernel=X is specified.
>  	crashkernel=size[KMG],low
> -			[KNL, X86-64] range under 4G. When crashkernel=X,high
> +			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
>  			is passed, kernel could allocate physical memory region
>  			above 4G, that cause second kernel crash on system
>  			that require some amount of low memory, e.g. swiotlb
> @@ -857,12 +857,6 @@
>  			It will be ignored when crashkernel=X,high is not used
>  			or memory reserved is below 4G.
>  
> -			[KNL, ARM64] range in low memory.
> -			This one lets the user specify a low range in the
> -			DMA zone for the crash dump kernel.
> -			It will be ignored when crashkernel=X,high is not used
> -			or memory reserved is located in the DMA zones.
> -
>  	cryptomgr.notests
>  			[KNL] Disable crypto self-tests
>  
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 339ee84e5a61a0b..5390f361208ccf7 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>  
> +/*
> + * This is an empirical value in x86_64 and taken here directly. Please
> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
> + * details.
> + */
> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
> +
>  static int __init reserve_crashkernel_low(unsigned long long low_size)
>  {
>  	unsigned long long low_base;
> @@ -147,7 +155,9 @@ static void __init reserve_crashkernel(void)
>  		 * is not allowed.
>  		 */
>  		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
> -		if (ret && (ret != -ENOENT))
> +		if (ret == -ENOENT)
> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +		else if (ret)
>  			return;

BTW, since we want a default low allocation, I think we should change
the checking logic slightly. Currently we have:

	if ((crash_base >= CRASH_ADDR_LOW_MAX) &&
	     crash_low_size && reserve_crashkernel_low(crash_low_size)) {
		...

If crash_base is just below CRASH_ADDR_LOW_MAX, we deem it sufficient
but a crashkernel trying to allocate 64MB of swiotlb may fail. So maybe
change this to crash_base >= CRASH_ADDR_LOW_MAX - crash_low_size.

-- 
Catalin

Re: [PATCH v3 2/2] arm64: kdump: Support crashkernel=X fall back to reserve region above DMA zones

[Leizhen (ThunderTown)]

On 2022/11/8 1:13, Catalin Marinas wrote:
> On Mon, Jul 11, 2022 at 05:03:19PM +0800, Zhen Lei wrote:
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 5390f361208ccf7..8539598f9e58b4d 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -138,6 +138,7 @@ static void __init reserve_crashkernel(void)
>>  	unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>>  	char *cmdline = boot_command_line;
>>  	int ret;
>> +	bool fixed_base;
>>  
>>  	if (!IS_ENABLED(CONFIG_KEXEC_CORE))
>>  		return;
>> @@ -166,15 +167,28 @@ static void __init reserve_crashkernel(void)
>>  		return;
>>  	}
>>  
>> +	fixed_base = !!crash_base;
>>  	crash_size = PAGE_ALIGN(crash_size);
>>  
>>  	/* User specifies base address explicitly. */
>> -	if (crash_base)
>> +	if (fixed_base)
>>  		crash_max = crash_base + crash_size;
> 
> Not a fan of '!!', it is converted automatically. If you don't like the
> conversion, just initialise fixed_base to false and here:
> 
> 	if (crash_base) {
> 		fixed_base = true;

OK, This way would be better.

> 		crash_max = crash_base + crash_size;
> 	}
> 
>> +retry:
>>  	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>>  					       crash_base, crash_max);
>>  	if (!crash_base) {
>> +		/*
>> +		 * Attempt to fully allocate low memory failed, fall back
>> +		 * to high memory, the minimum required low memory will be
>> +		 * reserved later.
>> +		 */
> 
> I'm not sure this comment makes sense. If !crash_base, it doesn't mean
> the kernel failed to fully allocate low memory. crash_max here could be
> CRASH_ADDR_HIGH_MAX if crashkerne=X,high was specified. Maybe says
> something like "If the first attempt was for low memory, fall back to
> high ..."

This description is accurate. I'll update. Thanks.

> 
>> +		if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
>> +			crash_max = CRASH_ADDR_HIGH_MAX;
>> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +			goto retry;
>> +		}
> 
> The retry logic looks fine, it only happens once as crash_max is
> updated.
> 

-- 
Regards,
  Zhen Lei

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Leizhen (ThunderTown)]

On 2022/11/8 1:18, Catalin Marinas wrote:
> On Mon, Jul 11, 2022 at 05:03:18PM +0800, Zhen Lei wrote:
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 2522b11e593f239..65a2c3a22a4b57d 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -843,7 +843,7 @@
>>  			available.
>>  			It will be ignored if crashkernel=X is specified.
>>  	crashkernel=size[KMG],low
>> -			[KNL, X86-64] range under 4G. When crashkernel=X,high
>> +			[KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high
>>  			is passed, kernel could allocate physical memory region
>>  			above 4G, that cause second kernel crash on system
>>  			that require some amount of low memory, e.g. swiotlb
>> @@ -857,12 +857,6 @@
>>  			It will be ignored when crashkernel=X,high is not used
>>  			or memory reserved is below 4G.
>>  
>> -			[KNL, ARM64] range in low memory.
>> -			This one lets the user specify a low range in the
>> -			DMA zone for the crash dump kernel.
>> -			It will be ignored when crashkernel=X,high is not used
>> -			or memory reserved is located in the DMA zones.
>> -
>>  	cryptomgr.notests
>>  			[KNL] Disable crypto self-tests
>>  
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 339ee84e5a61a0b..5390f361208ccf7 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>>  
>> +/*
>> + * This is an empirical value in x86_64 and taken here directly. Please
>> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
>> + * details.
>> + */
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
>> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
>> +
>>  static int __init reserve_crashkernel_low(unsigned long long low_size)
>>  {
>>  	unsigned long long low_base;
>> @@ -147,7 +155,9 @@ static void __init reserve_crashkernel(void)
>>  		 * is not allowed.
>>  		 */
>>  		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
>> -		if (ret && (ret != -ENOENT))
>> +		if (ret == -ENOENT)
>> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>> +		else if (ret)
>>  			return;
> 
> BTW, since we want a default low allocation, I think we should change
> the checking logic slightly. Currently we have:
> 
> 	if ((crash_base >= CRASH_ADDR_LOW_MAX) &&
> 	     crash_low_size && reserve_crashkernel_low(crash_low_size)) {
> 		...
> 
> If crash_base is just below CRASH_ADDR_LOW_MAX, we deem it sufficient
> but a crashkernel trying to allocate 64MB of swiotlb may fail. So maybe
> change this to crash_base >= CRASH_ADDR_LOW_MAX - crash_low_size.

The equal sign needs to be removed.

The situation should be the allocation of "crashkernel=X,high".

This possibility is too small, the high memory is unlikely to be that small.
memblock_phys_alloc_range() always search for memory block from high addresses
to low addresses. In the initial phase, high-end memory is not fragmented.

Of course, the modification can make people look more reassuring. OK, I'll
update it.

> 

-- 
Regards,
  Zhen Lei

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Will Deacon]

On Mon, Jul 11, 2022 at 05:03:17PM +0800, Zhen Lei wrote:
> v2 --> v3:
> 1. Discard patch 3 in v2, a cleanup patch.

Do you plan to respin this series, addressing the various comments on v3?

Will

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Leizhen (ThunderTown)]

On 2022/11/15 19:58, Will Deacon wrote:
> On Mon, Jul 11, 2022 at 05:03:17PM +0800, Zhen Lei wrote:
>> v2 --> v3:
>> 1. Discard patch 3 in v2, a cleanup patch.
> 
> Do you plan to respin this series, addressing the various comments on v3?

Yes, I haven't figured out where to make DEFAULT_CRASH_KERNEL_LOW_SIZE generic.

> 
> Will
> .
> 

-- 
Regards,
  Zhen Lei

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Catalin Marinas]

On Tue, Nov 15, 2022 at 08:18:21PM +0800, Leizhen (ThunderTown) wrote:
> On 2022/11/15 19:58, Will Deacon wrote:
> > On Mon, Jul 11, 2022 at 05:03:17PM +0800, Zhen Lei wrote:
> >> v2 --> v3:
> >> 1. Discard patch 3 in v2, a cleanup patch.
> > 
> > Do you plan to respin this series, addressing the various comments on v3?
> 
> Yes, I haven't figured out where to make DEFAULT_CRASH_KERNEL_LOW_SIZE generic.

Do we need to? I'd just go with something like 128MB, specific to arm64,
and we can increase it later if anyone comes up with a good argument.

-- 
Catalin

Re: [PATCH v3 0/2] arm64: kdump: Function supplement and performance optimization

[Leizhen (ThunderTown)]

On 2022/11/15 21:30, Catalin Marinas wrote:
> On Tue, Nov 15, 2022 at 08:18:21PM +0800, Leizhen (ThunderTown) wrote:
>> On 2022/11/15 19:58, Will Deacon wrote:
>>> On Mon, Jul 11, 2022 at 05:03:17PM +0800, Zhen Lei wrote:
>>>> v2 --> v3:
>>>> 1. Discard patch 3 in v2, a cleanup patch.
>>>
>>> Do you plan to respin this series, addressing the various comments on v3?
>>
>> Yes, I haven't figured out where to make DEFAULT_CRASH_KERNEL_LOW_SIZE generic.
> 
> Do we need to? I'd just go with something like 128MB, specific to arm64,
> and we can increase it later if anyone comes up with a good argument.

Okay, then v3's easy. I'll do it tomorrow. I've tried it before. 128M is enough.

> 

-- 
Regards,
  Zhen Lei

Re: [PATCH v3 1/2] arm64: kdump: Provide default size when crashkernel=Y,low is not specified

[Leizhen (ThunderTown)]

On 2022/11/7 22:07, Catalin Marinas wrote:
> On Mon, Jul 11, 2022 at 05:03:18PM +0800, Zhen Lei wrote:
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 339ee84e5a61a0b..5390f361208ccf7 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -96,6 +96,14 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1;
>>  #define CRASH_ADDR_LOW_MAX		arm64_dma_phys_limit
>>  #define CRASH_ADDR_HIGH_MAX		(PHYS_MASK + 1)
>>  
>> +/*
>> + * This is an empirical value in x86_64 and taken here directly. Please
>> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
>> + * details.
>> + */
>> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE	\
>> +	max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
> 
> I agree with Will here, we need a better comment and we might as well
> change the default value to something else until someone tells us that
> the default is not large enough. The default swiotlb size is 64M, so we
> need to cover that. The extra 8MB for any additional low allocations are
> ok as well but the 256MB doesn't make much sense to me, or at least not
> together with the rest.
> 
> If the main kernel got a command line option for a larger swiotlb, does
> the crash kernel boot with the same command line? If not, we can just go

Sometimes the image is shared, but the command line is often different.
The command line of the crash kernel is specified by kexec --append=.

> for a fixed 128M value here, which is double the default swiotlb buffer.

Sorry, I missed this e-mail. Yes, fixed 128M would be better. I haven't
seen anyone adding "swiotlb=" to the crash kernel. And, if the default size
isn't enough, he can use crashkernel=Y,low.

> 

-- 
Regards,
  Zhen Lei