linux-kernel - [PATCH v2] mm: align larger anonymous mappings on THP boundaries

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Message-ID: <20220809142457.4751229f@imladris.surriel.com>
Date:   Tue, 9 Aug 2022 14:24:57 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, Matthew Wilcox <willy@...radead.org>,
        Yang Shi <shy828301@...il.com>
Subject: [PATCH v2] mm: align larger anonymous mappings on THP boundaries

Align larger anonymous memory mappings on THP boundaries by
going through thp_get_unmapped_area if THPs are enabled for
the current process.

With this patch, larger anonymous mappings are now THP aligned.
When a malloc library allocates a 2MB or larger arena, that
arena can now be mapped with THPs right from the start, which
can result in better TLB hit rates and execution time.

Signed-off-by: Rik van Riel <riel@...riel.com>
---
v2: avoid the chicken & egg issue with MMF_VM_HUGEPAGE (Yang Shi)

 mm/mmap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index c035020d0c89..1d859893436d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2229,6 +2229,9 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 		 */
 		pgoff = 0;
 		get_area = shmem_get_unmapped_area;
+	} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+		/* Ensures that larger anonymous mappings are THP aligned. */
+		get_area = thp_get_unmapped_area;
 	}
 
 	addr = get_area(file, addr, len, pgoff, flags);
-- 
2.37.1