On 4/9/20 5:58 PM, Peter Xu wrote: > 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" There is an ongoing discussion to fix this issue. AFAIK it has not been settled yet and Mike was going to post a patch-set. https://lkml.org/lkml/2020/3/9/96 > > 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. -- Nitesh
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