linux-kernel - [PATCH] mm: hugetlb: fix per-node size calculation for hugetlb

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Message-ID: <20200323221411.2152675-1-guro@fb.com>
Date:   Mon, 23 Mar 2020 15:14:11 -0700
From:   Roman Gushchin <guro@...com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Aslan Barkirov <aslan@...com>, Michal Hocko <mhocko@...nel.org>,
        <linux-mm@...ck.org>, <kernel-team@...com>,
        <linux-kernel@...r.kernel.org>, Rik van Riel <riel@...riel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Roman Gushchin <guro@...com>
Subject: [PATCH] mm: hugetlb: fix per-node size calculation for hugetlb_cma

Aslan found a bug in the per-node hugetlb_cma area size calculation:
the total remaining size should cap the per-node area size instead
of be the minimal possible allocation.

Without the fix:
[    0.004136] hugetlb_cma: reserve 2048 MiB, up to 1024 MiB per node
[    0.004138] cma: Reserved 2048 MiB at 0x0000000180000000
[    0.004139] hugetlb_cma: reserved 2048 MiB on node 0

With the fix:
[    0.006780] hugetlb_cma: reserve 2048 MiB, up to 1024 MiB per node
[    0.006786] cma: Reserved 1024 MiB at 0x00000001c0000000
[    0.006787] hugetlb_cma: reserved 1024 MiB on node 0
[    0.006788] cma: Reserved 1024 MiB at 0x00000003c0000000
[    0.006789] hugetlb_cma: reserved 1024 MiB on node 1

Reported-by: Aslan Barkirov <aslan@...com>
Signed-off-by: Roman Gushchin <guro@...com>
---
 mm/hugetlb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 456f4c010fea..44b47c2b6fab 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5590,7 +5590,7 @@ void __init hugetlb_cma_reserve(int order)
 		min_pfn = min_low_pfn;
 		max_pfn = max_low_pfn;
 #endif
-		size = max(per_node, hugetlb_cma_size - reserved);
+		size = min(per_node, hugetlb_cma_size - reserved);
 		size = round_up(size, PAGE_SIZE << order);
 
 		if (size > ((max_pfn - min_pfn) << PAGE_SHIFT) / 2) {
-- 
2.25.1