On Thu, May 12, 2022 at 03:04:57PM +0200, David Hildenbrand wrote: > On 12.05.22 14:50, Muchun Song wrote: > > On Thu, May 12, 2022 at 09:36:15AM +0200, David Hildenbrand wrote: > >> On 09.05.22 08:27, Muchun Song wrote: > >>> Optimizing HugeTLB vmemmap pages is not compatible with allocating memmap on > >>> hot added memory. If "hugetlb_free_vmemmap=on" and > >>> memory_hotplug.memmap_on_memory" are both passed on the kernel command line, > >>> optimizing hugetlb pages takes precedence. > >> > >> Why? > >> > > > > Because both two features are not compatible since hugetlb_free_vmemmap cannot > > optimize the vmemmap pages allocated from alternative allocator (when > > memory_hotplug.memmap_on_memory=1). So when the feature of hugetlb_free_vmemmap > > is introduced, I made hugetlb_free_vmemmap take precedence. BTW, I have a plan > > to remove this restriction, I'll post it out ASAP. > > I was asking why vmemmap optimization should take precedence. > memmap_on_memory makes it more likely to succeed memory hotplug in > close-to-OOM situations -- which is IMHO more important than a vmemmap > optimization. > I thought the users who enable hugetlb_free_vmemmap value memory savings more, so I made a decision in commit 4bab4964a59f. Seems I made a bad decision from your description. > But anyhow, the proper approach should most probably be to simply not > mess with the vmemmap if we stumble over a vmemmap that's special due to > memmap_on_memory. I assume that's what you're talking about sending out. > I mean I want to have hugetlb_vmemmap.c do the check whether the section which the HugeTLB pages belong to can be optimized instead of making hugetlb_free_vmemmap take precedence. E.g. If the section's vmemmap pages are allocated from the added memory block itself, hugetlb_free_vmemmap will refuse to optimize the vmemmap, otherwise, do the optimization. Then both kernel parameters are compatible. I have done those patches, but haven't send them out. Thanks.
