linux-kernel - [PATCH] mm: hugetlb_vmemmap: provide stronger vmemmap allocaction gurantees

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Message-Id: <20230412152337.1203254-1-pasha.tatashin@soleen.com>
Date:   Wed, 12 Apr 2023 15:23:37 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        mike.kravetz@...cle.com, muchun.song@...ux.dev,
        rientjes@...gle.com, souravpanda@...gle.com
Subject: [PATCH] mm: hugetlb_vmemmap: provide stronger vmemmap allocaction gurantees

HugeTLB pages have a struct page optimizations where struct pages for tail
pages are freed. However, when HugeTLB pages are destroyed, the memory for
struct pages (vmemmap) need to be allocated again.

Currently, __GFP_NORETRY flag is used to allocate the memory for vmemmap,
but given that this flag makes very little effort to actually reclaim
memory the returning of huge pages back to the system can be problem. Lets
use __GFP_RETRY_MAYFAIL instead. This flag is also performs graceful
reclaim without causing ooms, but at least it may perform a few retries,
and will fail only when there is genuinely little amount of unused memory
in the system.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Suggested-by: David Rientjes <rientjes@...gle.com>
---
 mm/hugetlb_vmemmap.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index a559037cce00..c4226d2af7cc 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -475,9 +475,12 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
 	 * the range is mapped to the page which @vmemmap_reuse is mapped to.
 	 * When a HugeTLB page is freed to the buddy allocator, previously
 	 * discarded vmemmap pages must be allocated and remapping.
+	 *
+	 * Use __GFP_RETRY_MAYFAIL to fail only when there is genuinely little
+	 * unused memory in the system.
 	 */
 	ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse,
-				  GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
+				  GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_THISNODE);
 	if (!ret) {
 		ClearHPageVmemmapOptimized(head);
 		static_branch_dec(&hugetlb_optimize_vmemmap_key);
-- 
2.40.0.577.gac1e443424-goog