On 2/27/19 1:51 PM, Oscar Salvador wrote: > On Thu, Feb 21, 2019 at 10:42:12AM +0100, Oscar Salvador wrote: >> [1] https://lore.kernel.org/patchwork/patch/998796/ >> >> Signed-off-by: Oscar Salvador <osalva...@suse.de> > > Any further comments on this? > I do have a "concern" I would like to sort out before dropping the RFC: > > It is the fact that unless we have spare gigantic pages in other notes, the > offlining operation will loop forever (until the customer cancels the > operation). > While I do not really like that, I do think that memory offlining should be > done > with some sanity, and the administrator should know in advance if the system > is going > to be able to keep up with the memory pressure, aka: make sure we got what we > need in > order to make the offlining operation to succeed. > That translates to be sure that we have spare gigantic pages and other nodes > can take them. > > Given said that, another thing I thought about is that we could check if we > have > spare gigantic pages at has_unmovable_pages() time. > Something like checking "h->free_huge_pages - h->resv_huge_pages > 0", and if > it > turns out that we do not have gigantic pages anywhere, just return as we have > non-movable pages.
Of course, that check would be racy. Even if there is an available gigantic page at has_unmovable_pages() time there is no guarantee it will be there when we want to allocate/use it. But, you would at least catch 'most' cases of looping forever. > But I would rather not convulate has_unmovable_pages() with such checks and > "trust" > the administrator. Agree -- Mike Kravetz
