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Thu, 30 Oct 2025 10:55:16 +0800 (CST) Received: from dggemv712-chm.china.huawei.com (unknown [10.1.198.32]) by mail.maildlp.com (Postfix) with ESMTPS id 5014F1400CA; Thu, 30 Oct 2025 10:56:41 +0800 (CST) Received: from kwepemq500010.china.huawei.com (7.202.194.235) by dggemv712-chm.china.huawei.com (10.1.198.32) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Thu, 30 Oct 2025 10:56:41 +0800 Received: from [10.173.125.37] (10.173.125.37) by kwepemq500010.china.huawei.com (7.202.194.235) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Thu, 30 Oct 2025 10:56:40 +0800 Subject: Re: [PATCH v2 1/1] mm/ksm: recover from memory failure on KSM page by migrating to healthy duplicate To: Long long Xia CC: , , , , , , , , Longlong Xia , , References: <20251016101813.484565-1-xialonglong2025@163.com> <20251016101813.484565-2-xialonglong2025@163.com> <7c069611-21e1-40df-bdb1-a3144c54507e@163.com> <394cb428-c37b-44c7-8367-4f76514a6322@163.com> From: Miaohe Lin Message-ID: <64953691-ce0e-71d9-1ab3-7f8cefd6ace4@huawei.com> Date: Thu, 30 Oct 2025 10:56:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <394cb428-c37b-44c7-8367-4f76514a6322@163.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.125.37] X-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To kwepemq500010.china.huawei.com (7.202.194.235) X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 508342000E X-Stat-Signature: fsqn1wiy5ytcz9iesddck75zchzbiz8d X-HE-Tag: 1761793005-135553 X-HE-Meta: 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 ByH/kLn6 HwAIxig8bbg5ad0fFt6ioxEkNi4dYD/VNcsAzhNSeMgx09tmEQxdqJeZY6twcfHgY83nHP3gnwCSTkVd2yuTublpI1YRVmMjETEI953QoY0kQMeJdbgXdp38H05X/Po5BcZiiDT4biezwjEjPcpfVjLmcHlpydeaVH0gexGi/hNHvnAjo5U9A1vxIXoRlQVamlpGlIflKVKO6SOxUXatU7EMt/+5AWqJ2BvnPQM4TQtUYGls1bZHshGnJQxz3rAxMxE9T2pFlnodf3Oqafl1P5A6Q7+awmIX9DyKeTDf9WReOmWk0uCWLAfc7Kh65lbm0IytT+1+t2QKSt5luXfsSrMH3e9rvaZ29dXYluNgdwh/QpZ7MpG+OjjrSFZP/uFGeApLD6TgTPiNd6rtSiqJojkIwZA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/10/29 15:12, Long long Xia wrote: > Thanks for the reply. > > > 在 2025/10/29 14:40, Miaohe Lin 写道: >> On 2025/10/28 15:54, Long long Xia wrote: >>> Thanks for the reply. >>> >>> 在 2025/10/23 19:54, Miaohe Lin 写道: >>>> On 2025/10/16 18:18, Longlong Xia wrote: >>>>> From: Longlong Xia >>>>> >>>>> When a hardware memory error occurs on a KSM page, the current >>>>> behavior is to kill all processes mapping that page. This can >>>>> be overly aggressive when KSM has multiple duplicate pages in >>>>> a chain where other duplicates are still healthy. >>>>> >>>>> This patch introduces a recovery mechanism that attempts to >>>>> migrate mappings from the failing KSM page to a newly >>>>> allocated KSM page or another healthy duplicate already >>>>> present in the same chain, before falling back to the >>>>> process-killing procedure. >>>>> >>>>> The recovery process works as follows: >>>>> 1. Identify if the failing KSM page belongs to a stable node chain. >>>>> 2. Locate a healthy duplicate KSM page within the same chain. >>>>> 3. For each process mapping the failing page: >>>>>      a. Attempt to allocate a new KSM page copy from healthy duplicate >>>>>         KSM page. If successful, migrate the mapping to this new KSM page. >>>>>      b. If allocation fails, migrate the mapping to the existing healthy >>>>>         duplicate KSM page. >>>>> 4. If all migrations succeed, remove the failing KSM page from the chain. >>>>> 5. Only if recovery fails (e.g., no healthy duplicate found or migration >>>>>      error) does the kernel fall back to killing the affected processes. >>>>> >>>>> Signed-off-by: Longlong Xia >>>> Thanks for your patch. Some comments below. >>>> >>>>> --- >>>>>    mm/ksm.c | 246 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>>>>    1 file changed, 246 insertions(+) >>>>> >>>>> diff --git a/mm/ksm.c b/mm/ksm.c >>>>> index 160787bb121c..9099bad1ab35 100644 >>>>> --- a/mm/ksm.c >>>>> +++ b/mm/ksm.c >>>>> @@ -3084,6 +3084,246 @@ void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc) >>>>>    } >>>>>      #ifdef CONFIG_MEMORY_FAILURE >>>>> +static struct ksm_stable_node *find_chain_head(struct ksm_stable_node *dup_node) >>>>> +{ >>>>> +    struct ksm_stable_node *stable_node, *dup; >>>>> +    struct rb_node *node; >>>>> +    int nid; >>>>> + >>>>> +    if (!is_stable_node_dup(dup_node)) >>>>> +        return NULL; >>>>> + >>>>> +    for (nid = 0; nid < ksm_nr_node_ids; nid++) { >>>>> +        node = rb_first(root_stable_tree + nid); >>>>> +        for (; node; node = rb_next(node)) { >>>>> +            stable_node = rb_entry(node, >>>>> +                    struct ksm_stable_node, >>>>> +                    node); >>>>> + >>>>> +            if (!is_stable_node_chain(stable_node)) >>>>> +                continue; >>>>> + >>>>> +            hlist_for_each_entry(dup, &stable_node->hlist, >>>>> +                    hlist_dup) { >>>>> +                if (dup == dup_node) >>>>> +                    return stable_node; >>>>> +            } > may I add cond_resched(); here ？ >>>>> +        } >>>>> +    } >>>> Would above multiple loops take a long time in some corner cases? >>> Thanks for the concern. >>> >>> I do some simple test。 >>> >>> Test 1: 10 Virtual Machines (Real-world Scenario) >>> Environment: 10 VMs (256MB each) with KSM enabled >>> >>> KSM State: >>> pages_sharing: 262,802 (≈1GB) >>> pages_shared: 17,374 （≈68MB） >>> pages_unshared = 124,057 (≈485MB) >>> total ≈1.5GB >>> chain_count = 9, not_chain_count = 17152 >>> Red-black tree nodes to traverse: >>> 17,161 (9 chains + 17,152 non-chains) >>> >>> Performance: >>> find_chain: 898 μs (0.9 ms) >>> collect_procs_ksm: 4,409 μs (4.4 ms) >>> Total memory failure handling: 6,135 μs (6.1 ms) >>> >>> >>> Test 2: 10GB Single Process (Extreme Case) >>> Environment: Single process with 10GB memory, >>> 1,310,720 page pairs (each pair identical, different from others) >>> >>> KSM State: >>> pages_sharing: 1,311,740 （≈5GB) >>> pages_shared: 1,310,724 （≈5GB) >>> pages_unshared = 0 >>> total ≈10GB >>> Red-black tree nodes to traverse: >>> 1,310,721 (1 chain + 1,310,720 non-chains) >>> >>> Performance: >>> find_chain: 28,822 μs (28.8 ms) >>> collect_procs_ksm: 45,944 μs (45.9 ms) >>> Total memory failure handling: 46,594 μs (46.6 ms) >> Thanks for your test. >> >>> Summary: >>> The find_chain function shows approximately linear scaling with the number of red-black tree nodes. >>> With a 76x increase in nodes (17,161 → 1,310,721), latency increased by 32x (898 μs → 28,822 μs). >>> representing 62% of total memory failure handling time (46.6ms). >>> However, since memory failures are rare events, this latency may be acceptable >>> as it does not impact normal system performance and only affects error recovery paths. >>> >> IMHO, the execution time of a kernel function must not be too long without any scheduling points. >> Otherwise it may affect the normal scheduling of the system and leads to something like performance >> fluctuation. Or am I miss something? >> >> Thanks. >> . > > I will add cond_resched()in the loop of red-black tree to allow scheduling in find_chain(), may be it is enough? It looks work to me. Thanks. .