On 10/11/19 3:39 PM, Guilherme G. Piccoli wrote: > Currently there are 2 ways for setting HugeTLB hugepages in kernel; either > users pass parameters on kernel command-line or they can write to sysfs > files (which is effectively the sysctl way). > > Kdump kernels won't benefit from hugepages - in fact it's quite opposite, > it may be the case hugepages on kdump kernel can lead to OOM if kernel > gets unable to allocate demanded pages due to the fact the preallocated > hugepages are consuming a lot of memory. > > This patch proposes a new kernel parameter to prevent the creation of > HugeTLB hugepages - we currently don't have a way to do that. We can > even have kdump scripts removing the kernel command-line options to > set hugepages, but it's not straightforward to prevent sysctl/sysfs > configuration, given it happens in later boot or anytime when the > system is running. > > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxxxxx> > --- > > About some decisions took in this patch: > > * early_param() was used because I couldn't find a way to enforce > parameters' ordering when using __setup(), and we need nohugepages > processed before all other hugepages options. I don't know much about early_param(), so I will assume this works as you describe. However, a quick grep shows hugepage options for ia64 also with early_param. > * The return when sysctl handler is prevented to progress due to > nohugepages is -EINVAL, but could be changed; I've just followed > present code there, but I'm OK changing that if we have suggestions. It looks like you only have short circuited/prevented nr_hugepages via sysfs/sysctl. Theoretically, one could set nr_overcommit_hugepages and still allocate hugetlb pages. So, if you REALLY want to shut things down you need to stop this as well. There is already a macro hugepages_supported() that can be set by arch specific code. I wonder how difficult it would be to 'overwrite' the macro if nohugepages is specified. Perhaps just a level of naming indirection. This would use the existing code to prevent all hugetlb usage. It seems like there may be some discussion about 'the right' way to do kdump. I can't add to that discussion, but if such an option as nohugepages is needed, I can help. -- Mike Kravetz
