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Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0X0FmuTa_1775100433 cluster:ay36) by smtp.aliyun-inc.com; Thu, 02 Apr 2026 11:27:18 +0800 From: "Huang, Ying" To: Donet Tom Cc: David Hildenbrand , Andrew Morton , Ingo Molnar , Peter Zijlstra , Ritesh Harjani , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baolin Wang , Ying Huang , Juri Lelli , Mel Gorman Subject: Re: [PATCH v2] memory tiering: Do not allow promotion if NUMA_BALANCING_MEMORY_TIERING is disabled In-Reply-To: <20260323094849.3903-1-donettom@linux.ibm.com> (Donet Tom's message of "Mon, 23 Mar 2026 04:48:49 -0500") References: <20260323094849.3903-1-donettom@linux.ibm.com> Date: Thu, 02 Apr 2026 11:27:13 +0800 Message-ID: <87wlyqt52m.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Stat-Signature: iegi7ef1g78ne8i5yewym5kocp7s313x X-Rspamd-Queue-Id: 0F90040003 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1775100442-146355 X-HE-Meta: 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 tGBz4VJo n/+AiZuEkaR4t4qPjiZGdZGGE2B8xH5l0Yzz+TTCjhtdGQI/AljdT7C0GJx4V/SnhllEKGmH7X1ZgSGZqL9LfxHfbQyn6wWQ23FU/lqt679EU37lXg9BXYh/j25QC+EQ5z0cF02fd2BHD85Vg01t2jTVJRc9YCjCCnabAWr6BIp9p242uOyJrHdL1xMzD5nzHQAkQkB0DBZcWx/yjjmzkjSKJ7a/tLxGhHV4zHweO72853sJbyDrVb+c4D2vdgKpexX/Zs9+QrXyJT1UdlqwvIDAoWBbXgF5mOlQKJTWl6NE7kTNZwB7AmqNlYtMjq2pQn7sXJnJrGoeFZ5iCvV8inQlAtPQi+/x2YuRrBBqGPv5UVdjm7RMTMJLKTp0163MK2azPoRjonbn6C7/KVLWYrgcHmI9LQy9+OjN/PwU/oxEyZLpASOkRfiB42g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Donet Tom writes: > In the current implementation, if NUMA_BALANCING_MEMORY_TIERING is > disabled and the pages are on the lower tier, the pages may still be > promoted. > > This happens because task_numa_work() updates the last_cpupid field to > record the last access time only when NUMA_BALANCING_MEMORY_TIERING is > enabled and the folio is on the lower tier. If > NUMA_BALANCING_MEMORY_TIERING is disabled, the last_cpupid field > can retains a valid last CPU id. > > In should_numa_migrate_memory(), the decision checks whether > NUMA_BALANCING_MEMORY_TIERING is disabled, the folio is on the lower > tier, and last_cpupid is invalid. However, the last_cpupid can be > valid when NUMA_BALANCING_MEMORY_TIERING is disabled, the condition > evaluates to false and migration is allowed. > > This patch prevents promotion when NUMA_BALANCING_MEMORY_TIERING is > disabled and the folio is on the lower tier. > > Behavior before this change: > ============================ > - If NUMA_BALANCING_NORMAL is enabled, migration occurs between > nodes within the same memory tier, and promotion from lower > tier to higher tier may also happen. > > - If NUMA_BALANCING_MEMORY_TIERING is enabled, promotion from > lower tier to higher tier nodes is allowed. > > Behavior after this change: > =========================== > - If NUMA_BALANCING_NORMAL is enabled, migration will occur only > between nodes within the same memory tier. > > - If NUMA_BALANCING_MEMORY_TIERING is enabled, promotion from lower > tier to higher tier nodes will be allowed. > > - If both NUMA_BALANCING_MEMORY_TIERING and NUMA_BALANCING_NORMAL are > enabled, both migration (same tier) and promotion (cross tier) are > allowed. > > Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency") > Signed-off-by: Donet Tom > --- > v1 -> v2 > ======== > 1. Dropped changes in task_numa_fault() since the original changes > already handle runtime disabling of NUMA_BALANCING_MEMORY_TIERING. > > v1 -> https://lore.kernel.org/all/20260320092251.1290207-1-donettom@linux.ibm.com/ > --- > kernel/sched/fair.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index bf948db905ed..4b43809a3fb1 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2024,8 +2024,12 @@ bool should_numa_migrate_memory(struct task_struct *p, struct folio *folio, > this_cpupid = cpu_pid_to_cpupid(dst_cpu, current->pid); > last_cpupid = folio_xchg_last_cpupid(folio, this_cpupid); > > + /* > + * Do not allow promotion if NUMA_BALANCING_MEMORY_TIERING is disabled > + * and the pages are on the lower tier. > + */ > if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING) && > - !node_is_toptier(src_nid) && !cpupid_valid(last_cpupid)) > + !node_is_toptier(src_nid)) > return false; > > /* No. Even if NUMA_BALANCING_MEMORY_TIERING is disabled, we should still allow migrate pages from lower tier to higher tier via NUMA_BALANCING_NORMAL. If we have precious DDR, why waste it? This follows the semantics of NUMA_BALANCING_NORMAL before introducing NUMA_BALANCING_MEMORY_TIERING. --- Best Regards, Huang, Ying