On Tue, Jun 28, 2022 at 08:38:08AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote: > On Mon, Jun 27, 2022 at 10:25:13AM -0700, Mike Kravetz wrote: > > On 06/27/22 06:02, HORIGUCHI NAOYA(堀口 直也) wrote: > > > On Fri, Jun 24, 2022 at 12:11:07PM -0700, Mike Kravetz wrote: > > > > On 06/24/22 08:34, HORIGUCHI NAOYA(堀口 直也) wrote: > > > > > On Fri, Jun 24, 2022 at 04:15:19PM +0800, Miaohe Lin wrote: > > > > > > On 2022/6/24 16:03, Muchun Song wrote: > > > > > > > On Fri, Jun 24, 2022 at 10:25:48AM +0800, Miaohe Lin wrote: > > > > > > >> On 2022/6/24 7:51, Naoya Horiguchi wrote: > > > > > > >>> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> > > > > > > >> > > > > > > >> IIUC it might be better to do the below check: > > > > > > >> /* > > > > > > >> * Cannot return gigantic pages currently if runtime gigantic page > > > > > > >> * allocation is not supported. > > > > > > >> */ > > > > > > >> if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported()) > > > > > > >> goto out; > > > > > > >> > > > > > > > > > > > > > > The change looks good to me. However, the comments above is unnecessary > > > > > > > since gigantic_page_runtime_supported() is straightforward. > > > > > > > > > > > > Agree. The comments can be removed. > > > > > > > > > > Thank you, both. Adding !gigantic_page_runtime_supported without comment > > > > > makes sense to me. > > > > > > > > The change above makes sense to me. However, ... > > > > > > > > If we make the change above, will we have the same strange situation described > > > > in the commit message when !gigantic_page_runtime_supported() is true? > > > > > > > > IIUC, !gigantic_page_runtime_supported implies that gigantic hugetlb > > > > pages can not be allocated or freed at run time. They can only be > > > > allocated at boot time. So, there should NEVER be surplus gigantic > > > > pages if !gigantic_page_runtime_supported(). > > > > > > I have the same understanding as the above. > > > > > > > To avoid this situation, > > > > perhaps we should change set_max_huge_pages as follows (not tested)? > > > > > > The suggested diff looks clearer about what it does, so I'd like to take it > > > in the next version. Then, what do we do on the "if (hstate_if_gigantic())" > > > check in return_unused_surplus_pages in the original suggestion? Should it > > > be kept as is, or removed, or checked with !gigantic_page_runtime_supported()? > > > I guess that the new checks prevent calling return_unused_surplus_pages() > > > during pool shrinking, so the check seems not necessary any more. > > > > My first thought was to keep the check in return_unused_surplus_pages() as it > > is called in other code paths. However, it SHOULD only try to free surplus > > hugetlb pages. With the modifications to set_max_huge_pages we will not > > have any surplus gigantic pages if !gigantic_page_runtime_supported, so > > the check can be removed. > > > > Also note that we never try to dynamically allocate surplus gigantic pages. > > This also is left over from the time when we could not easily allocate a > > gigantic page at runtime. It would not surprise me if someone found a use > > case to ease this restriction in the future. Especially so if 1G THP support > > is ever added. If this happens, the check would be necessary and I would > > guess that it would not be added. > > > > Sorry for thinking our loud!!! Although not necessary, it 'might' be a good > > idea to leave the check because it would be overlooked if dynamic allocation > > of gigantic surplus pages is ever added. I do not have a strong opinion. > > OK, so let's keep the check. Sorry, I found that keeping the check doesn't fix the problem. I'll update the check with !gigantic_page_runtime_supported(). - Naoya Horiguchi
