[PATCH] mm/vmalloc: fix numa spreading for large hash tables

[Chen Wandun]

Eric Dumazet reported a strange numa spreading info in [1], and found
commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings") introduced
this issue [2].

Dig into the difference before and after this patch, page allocation has
some difference:

before:
alloc_large_system_hash
    __vmalloc
        __vmalloc_node(..., NUMA_NO_NODE, ...)
            __vmalloc_node_range
                __vmalloc_area_node
                    alloc_page /* because NUMA_NO_NODE, so choose alloc_page branch */
                        alloc_pages_current
                            alloc_page_interleave /* can be proved by print policy mode */

after:
alloc_large_system_hash
    __vmalloc
        __vmalloc_node(..., NUMA_NO_NODE, ...)
            __vmalloc_node_range
                __vmalloc_area_node
                    alloc_pages_node /* choose nid by nuam_mem_id() */
                        __alloc_pages_node(nid, ....)

So after commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings"),
it will allocate memory in current node instead of interleaving allocate
memory.

[1]
https://lore.kernel.org/linux-mm/CANn89iL6AAyWhfxdHO+jaT075iOa3XcYn9k6JJc7JR2XYn6k_Q@xxxxxxxxxxxxxx/

[2]
https://lore.kernel.org/linux-mm/CANn89iLofTR=AK-QOZY87RdUZENCZUT4O6a0hvhu3_EwRMerOg@xxxxxxxxxxxxxx/

Fixes: 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings")
Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Chen Wandun <chenwandun@xxxxxxxxxx>
---
 mm/vmalloc.c | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f884706c5280..48e717626e94 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2823,6 +2823,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 		unsigned int order, unsigned int nr_pages, struct page **pages)
 {
 	unsigned int nr_allocated = 0;
+	struct page *page;
+	int i;
 
 	/*
 	 * For order-0 pages we make use of bulk allocator, if
@@ -2833,6 +2835,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 	if (!order) {
 		while (nr_allocated < nr_pages) {
 			unsigned int nr, nr_pages_request;
+			page = NULL;
 
 			/*
 			 * A maximum allowed request is hard-coded and is 100
@@ -2842,9 +2845,23 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 			 */
 			nr_pages_request = min(100U, nr_pages - nr_allocated);
 
-			nr = alloc_pages_bulk_array_node(gfp, nid,
-				nr_pages_request, pages + nr_allocated);
-
+			if (nid == NUMA_NO_NODE) {
+				for (i = 0; i < nr_pages_request; i++) {
+					page = alloc_page(gfp);
+					if (page)
+						pages[nr_allocated + i] = page;
+					else {
+						nr = i;
+						break;
+					}
+				}
+				if (i >= nr_pages_request)
+					nr = nr_pages_request;
+			} else {
+				nr = alloc_pages_bulk_array_node(gfp, nid,
+							nr_pages_request,
+							pages + nr_allocated);
+			}
 			nr_allocated += nr;
 			cond_resched();
 
@@ -2863,11 +2880,13 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
 		gfp |= __GFP_COMP;
 
 	/* High-order pages or fallback path if "bulk" fails. */
-	while (nr_allocated < nr_pages) {
-		struct page *page;
-		int i;
 
-		page = alloc_pages_node(nid, gfp, order);
+	page = NULL;
+	while (nr_allocated < nr_pages) {
+		if (nid == NUMA_NO_NODE)
+			page = alloc_pages(gfp, order);
+		else
+			page = alloc_pages_node(nid, gfp, order);
 		if (unlikely(!page))
 			break;
 
-- 
2.25.1