Hi Mel, On Thu, Nov 26, 2020 at 10:47:20AM +0000, Mel Gorman wrote: > Agreed. This thread has a lot of different directions in it at this > point so what I'd hope for is first, a patch that initialises holes with > zone/node linkages within a 1<<(MAX_ORDER-1) alignment. If there is a > hole, it would be expected the pages are PageReserved. Second, a fix to > fast_isolate that forces PFNs returned to always be within the stated > zone boundaries. The last two patches should resolve the struct page initialization https://git.kernel.org/pub/scm/linux/kernel/git/andrea/aa.git/ and the VM_BUG_ON_PAGE never happened again as expected. So I looked back to see how the "distance" logic is accurate. I added those checks and I get negative hits: diff --git a/mm/compaction.c b/mm/compaction.c index cc1a7f600a86..844a90b0acdf 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1331,6 +1331,12 @@ fast_isolate_freepages(struct compact_control *cc) low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2)); min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1)); + WARN_ON_ONCE((long) low_pfn < 0); + WARN_ON_ONCE((long) min_pfn < 0); + if ((long) low_pfn < 0) + return cc->free_pfn; + if ((long) min_pfn < 0) + return cc->free_pfn; if (WARN_ON_ONCE(min_pfn > low_pfn)) low_pfn = min_pfn; Both warn-on-once triggers, so it goes negative. While it appears not kernel crashing since pfn_valid won't succeed on negative entries and they'll always be higher than any pfn in the freelist, is this sign that there's further room for improvement here? Thanks, Andrea
