The hugepage options are not documented clearly. Firstly, default_hugepagesz= should always be specified after the declaration of the same type of huge page using hugepagesz=. For example, if we boot a x86_64 system with kernel cmdline "default_hugepagesz=2M", we'll get a very funny error message: "HugeTLB: unsupported default_hugepagesz 2097152. Reverting to 2097152" It's understandable from code-wise because when hugetlb_init() we didn't have the 2M page hstate registered, so it's unsupported. However 2M is actually the default huge page size on x86_64, so we'll register it right after the error message. However it's very confusing if without these knowledges. Secondly, hugepages= option must be used _after_ another hugepagesz=. The word "interleave" is fine but it didn't declare the fact that each of the hugepages= option will be applied to the previous parsed hugepagesz= option. State all these clear. Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> --- .../admin-guide/kernel-parameters.txt | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 86aae1fa099a..2a77b2b01e5e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -839,7 +839,8 @@ the legacy /proc/ hugepages APIs, used for SHM, and default size when mounting hugetlbfs filesystems. Defaults to the default architecture's huge page size - if not specified. + if not specified. This option can only be used with a + pre-defined "hugepagesz=" of the same size. deferred_probe_timeout= [KNL] Debugging option to set a timeout in seconds for @@ -1475,13 +1476,17 @@ hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET registers. Default set by CONFIG_HPET_MMAP_DEFAULT. + hugepagesz= [HW,IA-64,PPC,X86-64] Declare one type of HugeTLB pages + with the size specified. Valid pages sizes on x86-64 + are 2M (when the CPU supports "pse") and 1G (when the + CPU supports the "pdpe1gb" cpuinfo flag). + hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. - hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. - On x86-64 and powerpc, this option can be specified - multiple times interleaved with hugepages= to reserve - huge pages of different sizes. Valid pages sizes on - x86-64 are 2M (when the CPU supports "pse") and 1G - (when the CPU supports the "pdpe1gb" cpuinfo flag). + On x86-64 and powerpc, this option must be used after + one hugepagesz= to allocate huge pages of that specific + size. This option can also be used multiple times + pairing with hugepagesz= to allocate huge pages for + different sizes. hung_task_panic= [KNL] Should the hung task detector generate panics. -- 2.24.1
