linux-kernel - [v3 2/2] mm: khugepaged: avoid overriding min_free

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Message-Id: <1600305709-2319-3-git-send-email-vijayb@linux.microsoft.com>
Date:   Wed, 16 Sep 2020 18:21:49 -0700
From:   Vijay Balakrishna <vijayb@...ux.microsoft.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Song Liu <songliubraving@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Vijay Balakrishna <vijayb@...ux.microsoft.com>,
        Michal Hocko <mhocko@...e.com>,
        Allen Pais <apais@...rosoft.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [v3 2/2] mm: khugepaged: avoid overriding min_free_kbytes set by user

set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
user.  Post start-of-day THP enable or memory hotplug operations can
lose user specified min_free_kbytes, in particular when it is higher than
calculated recommended value.  user_min_free_kbytes initialized to 0
to avoid undesired result when comparing with  "unsigned long" type.

Signed-off-by: Vijay Balakrishna <vijayb@...ux.microsoft.com>
Cc: stable@...r.kernel.org
Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>
---
 mm/khugepaged.c | 3 ++-
 mm/page_alloc.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4f7107476a6f..3c1147816d12 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2283,7 +2283,8 @@ static void set_recommended_min_free_kbytes(void)
 			      (unsigned long) nr_free_buffer_pages() / 20);
 	recommended_min <<= (PAGE_SHIFT-10);
 
-	if (recommended_min > min_free_kbytes) {
+	if (recommended_min > min_free_kbytes ||
+		recommended_min > user_min_free_kbytes) {
 		if (user_min_free_kbytes >= 0)
 			pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
 				min_free_kbytes, recommended_min);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fab5e97dc9ca..7b81fb139034 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -315,7 +315,7 @@ compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {
 };
 
 int min_free_kbytes = 1024;
-int user_min_free_kbytes = -1;
+int user_min_free_kbytes = 0;
 #ifdef CONFIG_DISCONTIGMEM
 /*
  * DiscontigMem defines memory ranges as separate pg_data_t even if the ranges
-- 
2.28.0