On Thu, May 28, 2020 at 2:50 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > On 5/28/20 11:15 AM, Holger Hoffstätte wrote: > > > > On 5/18/20 8:14 PM, Nitin Gupta wrote: > > [patch v5 :)] > > > > I've been successfully using this in my tree and it works great, but a friend > > who also uses my tree just found a bug (actually an improvement ;) due to the > > change from HUGETLB_PAGE_ORDER to HPAGE_PMD_ORDER in v5. > > > > When building with CONFIG_TRANSPARENT_HUGEPAGE=n (for some reason it was off) > > HPAGE_PMD_SHIFT expands to BUILD_BUG() and compilation fails like this: > > Oops, I forgot about this. Still I believe HPAGE_PMD_ORDER is the best choice as > long as THP's are enabled. I guess fallback to HUGETLB_PAGE_ORDER would be > possible if THPS are not enabled, but AFAICS some architectures don't define > that. Such architectures perhaps won't benefit from proactive compaction anyway? > I am not sure about such architectures but in such cases, we would end up calculating "fragmentation score" based on a page size which does not match the architecture's view of the "default hugepage size" which is not a terrible thing in itself as compaction can still be done in the background, after all. Since we always need a target order to calculate the fragmentation score, how about this fallack scheme: HPAGE_PMD_ORDER -> HUGETLB_PAGE_ORDER -> PMD_ORDER Thanks, Nitin
