The patch titled
Subject: mm/cma.c: use exact_nid true to fix possible per-numa cma leak
has been added to the -mm tree. Its filename is
mm-cmac-use-exact_nid-true-to-fix-possible-per-numa-cma-leak.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-cmac-use-exact_nid-true-to-fix-possible-per-numa-cma-leak.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-cmac-use-exact_nid-true-to-fix-possible-per-numa-cma-leak.patch
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From: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
Subject: mm/cma.c: use exact_nid true to fix possible per-numa cma leak
Calling cma_declare_contiguous_nid() with false exact_nid for per-numa
reservation can easily cause cma leak and various confusion. For example,
mm/hugetlb.c is trying to reserve per-numa cma for gigantic pages. But it
can easily leak cma and make users confused when system has memoryless
nodes.
In case the system has 4 numa nodes, and only numa node0 has memory. if
we set hugetlb_cma=4G in bootargs, mm/hugetlb.c will get 4 cma areas for 4
different numa nodes. since exact_nid=false in current code, all 4 numa
nodes will get cma successfully from node0, but hugetlb_cma[1 to 3] will
never be available to hugepage will only allocate memory from
hugetlb_cma[0].
In case the system has 4 numa nodes, both numa node0&2 has memory, other
nodes have no memory. if we set hugetlb_cma=4G in bootargs, mm/hugetlb.c
will get 4 cma areas for 4 different numa nodes. since exact_nid=false in
current code, all 4 numa nodes will get cma successfully from node0 or 2,
but hugetlb_cma[1] and [3] will never be available to hugepage as
mm/hugetlb.c will only allocate memory from hugetlb_cma[0] and
hugetlb_cma[2]. This causes permanent leak of the cma areas which are
supposed to be used by memoryless node.
Of cource we can workaround the issue by letting mm/hugetlb.c scan all cma
areas in alloc_gigantic_page() even node_mask includes node0 only. that
means when node_mask includes node0 only, we can get page from
hugetlb_cma[1] to hugetlb_cma[3]. But this will cause kernel crash in
free_gigantic_page() while it wants to free page by:
cma_release(hugetlb_cma[page_to_nid(page)], page, 1 << order)
On the other hand, exact_nid=false won't consider numa distance, it might
be not that useful to leverage cma areas on remote nodes. I feel it is
much simpler to make exact_nid true to make everything clear. After that,
memoryless nodes won't be able to reserve per-numa CMA from other nodes
which have memory.
Link: http://lkml.kernel.org/r/20200628074345.27228-1-song.bao.hua@xxxxxxxxxxxxx
Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma")
Signed-off-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
Acked-by: Roman Gushchin <guro@xxxxxx>
Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Cc: Aslan Bakirov <aslan@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Andreas Schaufler <andreas.schaufler@xxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Joonsoo Kim <js1304@xxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/cma.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/cma.c~mm-cmac-use-exact_nid-true-to-fix-possible-per-numa-cma-leak
+++ a/mm/cma.c
@@ -339,13 +339,13 @@ int __init cma_declare_contiguous_nid(ph
*/
if (base < highmem_start && limit > highmem_start) {
addr = memblock_alloc_range_nid(size, alignment,
- highmem_start, limit, nid, false);
+ highmem_start, limit, nid, true);
limit = highmem_start;
}
if (!addr) {
addr = memblock_alloc_range_nid(size, alignment, base,
- limit, nid, false);
+ limit, nid, true);
if (!addr) {
ret = -ENOMEM;
goto err;
_
Patches currently in -mm which might be from song.bao.hua@xxxxxxxxxxxxx are
mm-cmac-use-exact_nid-true-to-fix-possible-per-numa-cma-leak.patch
mm-cma-fix-the-name-of-cma-areas.patch
mm-hugetlb-fix-the-name-of-hugetlb-cma.patch
