From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout02.his.huawei.com (canpmsgout02.his.huawei.com [113.46.200.217]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ABC112F3C2C for ; Thu, 30 Oct 2025 02:56:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.217 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761793006; cv=none; b=dPECrfUzWq82mbanpZOWeC3R1Qf7MNsk2YRkJbLXuGMERzWxogG6Ye61ulUGDBe19BFnyYP2bB/nvUfkUFGyTvK4z71rf+Z1BJ2Ic4QSBQf2MgrmlZT/3EPWpNpJpsADNlZDjNmKsz54ShUOlhpGSK4VPYe/qLoi5XNbQhdJbPk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761793006; c=relaxed/simple; bh=quWH6eCcrNC5UfTsSZ1/it88qcWGG9o4SZYqIH746zs=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=aARIZ7Btx8DQ/LWMkRfzZ1vAz2EKZmrgsy5wSZawwcvmoc7rf2krJMxYog8R9715QznjCAhCrS75Jse42aeTzMSHJurgCJ+1c4ijowSkaMpsC+blKSfYwfM6ssgaWGcVXxI+tpHq90f5Sv9lOWfGRbHlan7MzjhgY0uoUQEwe/A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=07btWpbi; arc=none smtp.client-ip=113.46.200.217 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="07btWpbi" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=0hQRTMFxdEmNDfeGmLa4tp3RC8FcGsqNeLnBB5VEq1c=; b=07btWpbiNwohyHweI9wu3LKC7j9YqX14x1hnrhD1+fM4hQbECyJblJChg2G+DUQNOyPl1NO3a +DhOrhcz9tOc0Af9ZY00AzcrDkVyplF1moRr/Up7Q8V067Tm13Y46+fC4fJqzhQd2YwVuikRMv3 FRrgWfU7FV8AfF/YLPrIiao= Received: from mail.maildlp.com (unknown [172.19.88.194]) by canpmsgout02.his.huawei.com (SkyGuard) with ESMTPS id 4cxpd00sztzcZyk; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To kwepemq500010.china.huawei.com (7.202.194.235) 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. .