On Mon, Sep 18, 2023 at 09:07:53AM +0200, Vlastimil Babka wrote: > On 9/15/23 16:16, Johannes Weiner wrote: > > On Thu, Sep 14, 2023 at 04:52:38PM -0700, Mike Kravetz wrote: > >> In next-20230913, I started hitting the following BUG. Seems related > >> to this series. And, if series is reverted I do not see the BUG. > >> > >> I can easily reproduce on a small 16G VM. kernel command line contains > >> "hugetlb_free_vmemmap=on hugetlb_cma=4G". Then run the script, > >> while true; do > >> echo 4 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages > >> echo 4 > /sys/kernel/mm/hugepages/hugepages-1048576kB/demote > >> echo 0 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages > >> done > >> > >> For the BUG below I believe it was the first (or second) 1G page creation from > >> CMA that triggered: cma_alloc of 1G. > >> > >> Sorry, have not looked deeper into the issue. > > > > Thanks for the report, and sorry about the breakage! > > > > I was scratching my head at this: > > > > /* MIGRATE_ISOLATE page should not go to pcplists */ > > VM_BUG_ON_PAGE(is_migrate_isolate(mt), page); > > > > because there is nothing in page isolation that prevents setting > > MIGRATE_ISOLATE on something that's on the pcplist already. So why > > didn't this trigger before already? > > > > Then it clicked: it used to only check the *pcpmigratetype* determined > > by free_unref_page(), which of course mustn't be MIGRATE_ISOLATE. > > > > Pages that get isolated while *already* on the pcplist are fine, and > > are handled properly: > > > > mt = get_pcppage_migratetype(page); > > > > /* MIGRATE_ISOLATE page should not go to pcplists */ > > VM_BUG_ON_PAGE(is_migrate_isolate(mt), page); > > > > /* Pageblock could have been isolated meanwhile */ > > if (unlikely(isolated_pageblocks)) > > mt = get_pageblock_migratetype(page); > > > > So this was purely a sanity check against the pcpmigratetype cache > > operations. With that gone, we can remove it. > > Agreed, I assume you'll fold it in 1/6 in v3. Yes, will do.
