Re: [Xen-devel] [libvirt] [PATCH 2/2] libxl: fix dom0 maximum memory setting

[Jim Fehlig <jfehlig@xxxxxxxx>]

Joao Martins wrote:
> On 02/02/2017 10:31 PM, Jim Fehlig wrote:
>> When the libxl driver is initialized, it creates a virDomainDef
>> object for dom0 and adds it to the list of domains. Total memory
>> for dom0 was being set from the max_memkb field of libxl_dominfo
>> struct retrieved from libxl, but this field can be set to
>> LIBXL_MEMKB_DEFAULT (~0ULL) if dom0 maximum memory has not been
>> explicitly set by the user.
>>
>> This patch adds some simple parsing of the Xen commandline,
>> looking for a dom0_mem parameter that also specifies a 'max' value.
>> If not specified, dom0 maximum memory is effectively all physical
>> host memory.
>>
>> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>
>> ---
>>  src/libxl/libxl_conf.c   | 75 
>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>  src/libxl/libxl_conf.h   |  3 ++
>>  src/libxl/libxl_driver.c |  2 +-
>>  3 files changed, 79 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
>> index b5186f2..bfe0e92 100644
>> --- a/src/libxl/libxl_conf.c
>> +++ b/src/libxl/libxl_conf.c
>> @@ -34,6 +34,7 @@
>>  #include "internal.h"
>>  #include "virlog.h"
>>  #include "virerror.h"
>> +#include "c-ctype.h"
>>  #include "datatypes.h"
>>  #include "virconf.h"
>>  #include "virfile.h"
>> @@ -1530,6 +1531,80 @@ int libxlDriverConfigLoadFile(libxlDriverConfigPtr 
>> cfg,
>>  
>>  }
>>  
>> +/*
>> + * dom0's maximum memory can be controled by the user with the 'dom0_mem' 
>> Xen
>> + * command line parameter. E.g. to set dom0's initial memory to 4G and max
>> + * memory to 8G: dom0_mem=4G,max:8G
>> + *
>> + * If not constrained by the user, dom0 can effectively use all host memory.
>> + * This function returns the configured maximum memory for dom0 in 
>> kilobytes,
>> + * either the user-specified value or total physical memory as a default.
>> + */
>> +unsigned long long
>> +libxlDriverGetDom0MaxmemConf(libxlDriverConfigPtr cfg)
>> +{
>> +    char **cmd_tokens = NULL;
>> +    char **mem_tokens = NULL;
>> +    size_t i;
>> +    size_t j;
>> +    unsigned long long ret;
>> +    libxl_physinfo physinfo;
>> +
>> +    if (cfg->verInfo->commandline == NULL ||
>> +        !(cmd_tokens = virStringSplit(cfg->verInfo->commandline, " ", 0)))
>> +        goto physmem;
>> +
>> +    for (i = 0; cmd_tokens[i] != NULL; i++) {
>> +        if (!STRPREFIX(cmd_tokens[i], "dom0_mem="))
>> +            continue;
>> +
>> +        if (!(mem_tokens = virStringSplit(cmd_tokens[i], ",", 0)))
>> +            break;
>> +        for (j = 0; mem_tokens[j] != NULL; j++) {
>> +            if (STRPREFIX(mem_tokens[j], "max:")) {
>> +                char *p = mem_tokens[j] + 4;
>> +                unsigned long long multiplier = 1;
>> +
>> +                while (c_isdigit(*p))
>> +                    p++;
>> +                if (virStrToLong_ull(mem_tokens[j] + 4, &p, 10, &ret) < 0)
>> +                    break;
>> +                if (*p) {
>> +                    switch (*p) {
>> +                    case 'k':
>> +                    case 'K':
>> +                        multiplier = 1024;
>> +                        break;
>> +                    case 'm':
>> +                    case 'M':
>> +                        multiplier = 1024 * 1024;
>> +                        break;
>> +                    case 'g':
>> +                    case 'G':
>> +                        multiplier = 1024 * 1024 * 1024;
>> +                        break;
>> +                    }
>> +                }
>> +                ret = (ret * multiplier) / 1024;
>> +                goto cleanup;
>> +            }
>> +        }
>> +    }
>> +
>> + physmem:
>> +    /* No 'max' specified in dom0_mem, so dom0 can use all physical memory 
>> */
>> +    libxl_physinfo_init(&physinfo);
>> +    libxl_get_physinfo(cfg->ctx, &physinfo);
> Despite being an unlikely event, libxl_get_physinfo can fail here - I think 
> you
> need to check the return value here.

Bummer. I was hoping this function could always return a sane value for dom0 max
memory. But I'm not really sure what that would be if libxl_get_physinfo failed.

> 
>> +    ret = (physinfo.total_pages * cfg->verInfo->pagesize) / 1024;
>> +    libxl_physinfo_dispose(&physinfo);
>> +
>> + cleanup:
>> +    virStringListFree(cmd_tokens);
>> +    virStringListFree(mem_tokens);
>> +    return ret;
>> +}
>> +
>> +
>>  #ifdef LIBXL_HAVE_DEVICE_CHANNEL
>>  static int
>>  libxlPrepareChannel(virDomainChrDefPtr channel,
>> diff --git a/src/libxl/libxl_conf.h b/src/libxl/libxl_conf.h
>> index 69d7885..c4ddbfe 100644
>> --- a/src/libxl/libxl_conf.h
>> +++ b/src/libxl/libxl_conf.h
>> @@ -173,6 +173,9 @@ libxlDriverNodeGetInfo(libxlDriverPrivatePtr driver,
>>  int libxlDriverConfigLoadFile(libxlDriverConfigPtr cfg,
>>                                const char *filename);
>>  
>> +unsigned long long
>> +libxlDriverGetDom0MaxmemConf(libxlDriverConfigPtr cfg);
>> +
>>  int
>>  libxlMakeDisk(virDomainDiskDefPtr l_dev, libxl_device_disk *x_dev);
>>  int
>> diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
>> index 921cc93..e54b3b7 100644
>> --- a/src/libxl/libxl_driver.c
>> +++ b/src/libxl/libxl_driver.c
>> @@ -615,7 +615,7 @@ libxlAddDom0(libxlDriverPrivatePtr driver)
>>      if (virDomainDefSetVcpus(vm->def, d_info.vcpu_online) < 0)
>>          goto cleanup;
>>      vm->def->mem.cur_balloon = d_info.current_memkb;
>> -    virDomainDefSetMemoryTotal(vm->def, d_info.max_memkb);
>> +    virDomainDefSetMemoryTotal(vm->def, libxlDriverGetDom0MaxmemConf(cfg));
> 
> And perhaps checking here too on whether "libxlDriverGetDom0MaxmemConf(cfg) < 
> 0" ?

ATM, libxlDriverGetDom0MaxmemConf returns an unsigned long long. I could change
the signature to

int
libxlDriverGetDom0MaxmemConf(libxlDriverConfigPtr cfg,
                             unsigned long long *maxmem)

but again I'm not really sure what to do with maxmem in case of failure. Perhaps
just set it to current_memkb?

Regards,
Jim


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