linux-kernel - Re: [PATCH 3/3] powerpc: Set crashkernel offset to mid of RMA region

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Date:   Tue, 5 Oct 2021 13:44:36 +0530
From:   Sourabh Jain <sourabhjain@...ux.ibm.com>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>, mpe@...erman.id.au
Cc:     Abdul haleem <abdhalee@...ux.vnet.ibm.com>,
        mahesh@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        hbathini@...ux.ibm.com, linuxppc-dev@...abs.org
Subject: Re: [PATCH 3/3] powerpc: Set crashkernel offset to mid of RMA region


On 04/10/21 21:36, Aneesh Kumar K.V wrote:
> On 10/4/21 20:41, Sourabh Jain wrote:
>> On large config LPARs (having 192 and more cores), Linux fails to boot
>> due to insufficient memory in the first memory block. It is due to the
>> reserve crashkernel area starts at 128MB offset by default and which
>> doesn't leave enough space in the first memory block to accommodate
>> memory for other essential system resources.
>>
>> Given that the RMA region size can be 512MB or more, setting the
>> crashkernel offset to mid of RMA size will leave enough space to
>> kernel to allocate memory for other system resources in the first
>> memory block.
>>
>> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
>> Reported-and-tested-by: Abdul haleem <abdhalee@...ux.vnet.ibm.com>
>> ---
>>   arch/powerpc/kernel/rtas.c |  3 +++
>>   arch/powerpc/kexec/core.c  | 13 +++++++++----
>>   2 files changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
>> index ff80bbad22a5..ce5e62bb4d8e 100644
>> --- a/arch/powerpc/kernel/rtas.c
>> +++ b/arch/powerpc/kernel/rtas.c
>> @@ -1235,6 +1235,9 @@ int __init early_init_dt_scan_rtas(unsigned 
>> long node,
>>       entryp = of_get_flat_dt_prop(node, "linux,rtas-entry", NULL);
>>       sizep  = of_get_flat_dt_prop(node, "rtas-size", NULL);
>>   +    if (of_get_flat_dt_prop(node, "ibm,hypertas-functions", NULL))
>> +        powerpc_firmware_features |= FW_FEATURE_LPAR;
>> +
>
> The equivalent check that we currently do more than checking 
> ibm,hypertas-functions.
>
>     if (!strcmp(uname, "rtas") || !strcmp(uname, "rtas@0")) {
>         prop = of_get_flat_dt_prop(node, "ibm,hypertas-functions",
>                        &len);
>         if (prop) {
>             powerpc_firmware_features |= FW_FEATURE_LPAR;
>             fw_hypertas_feature_init(prop, len);
>         }
>
>
> also do we expect other firmware features to be set along with 
> FW_FEATURE_LPAR?

This patch needs to move crash kernel reservation to mid point of rma 
size for LPAR in reserve_crashkernel() function. Since 
reserve_crashkernel() is called too early even before 
powerpc_firmware_features is set with FW_FEATURE_LPAR, the check for if 
(firmware_has_feature(FW_FEATURE_LPAR)) fails and hence we only need to 
make sure that we set this flag early during early_init_dt_scan_rtas().

The rest of the LPAR specific initialization isn't required at this 
point and will be still done during pseries_probe_fw_features() as usual.

Thanks,
Sourabh Jain