For systems configured to always try hard to allocate transparent hugepages (thp defrag setting of "always") or for memory that has been explicitly madvised to MADV_HUGEPAGE, it is often better to fallback to remote memory to allocate the hugepage if the local allocation fails first. The point is to allow the initial call to __alloc_pages_node() to attempt to defragment local memory to make a hugepage available, if possible, rather than immediately fallback to remote memory. Local hugepages will always have a better access latency than remote (huge)pages, so an attempt to make a hugepage available locally is always preferred. If memory compaction cannot be successful locally, however, it is likely better to fallback to remote memory. This could take on two forms: either allow immediate fallback to remote memory or do per-zone watermark checks. It would be possible to fallback only when per-zone watermarks fail for order-0 memory, since that would require local reclaim for all subsequent faults so remote huge allocation is likely better than thrashing the local zone for large workloads. In this case, it is assumed that because the system is configured to try hard to allocate hugepages or the vma is advised to explicitly want to try hard for hugepages that remote allocation is better when local allocation and memory compaction have both failed. Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx> --- mm/mempolicy.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/mempolicy.c b/mm/mempolicy.c --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2133,6 +2133,17 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma, mpol_cond_put(pol); page = __alloc_pages_node(hpage_node, gfp | __GFP_THISNODE, order); + + /* + * If hugepage allocations are configured to always + * synchronous compact or the vma has been madvised + * to prefer hugepage backing, retry allowing remote + * memory as well. + */ + if (!page && (gfp & __GFP_DIRECT_RECLAIM)) + page = __alloc_pages_node(hpage_node, + gfp | __GFP_NORETRY, order); + goto out; } }
