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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-429952ca979sm19799481f8f.14.2025.10.28.02.44.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Oct 2025 02:44:38 -0700 (PDT) Message-ID: Date: Tue, 28 Oct 2025 10:44:37 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] mm/ksm: recover from memory failure on KSM page by migrating to healthy duplicate To: Longlong Xia , linmiaohe@huawei.com, lance.yang@linux.dev Cc: markus.elfring@web.de, nao.horiguchi@gmail.com, akpm@linux-foundation.org, wangkefeng.wang@huawei.com, qiuxu.zhuo@intel.com, xu.xin16@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Longlong Xia References: <20251016101813.484565-1-xialonglong2025@163.com> <20251016101813.484565-2-xialonglong2025@163.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20251016101813.484565-2-xialonglong2025@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 16.10.25 12:18, 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 > --- > 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); Put that into a single line for readability, please. You can also consider factoring out this inner loop in a helper function. > + > + if (!is_stable_node_chain(stable_node)) > + continue; > + > + hlist_for_each_entry(dup, &stable_node->hlist, > + hlist_dup) { Single line, or properly indent. > + if (dup == dup_node) > + return stable_node; > + } > + } > + } > + > + return NULL; > +} > + > +static struct folio *find_healthy_folio(struct ksm_stable_node *chain_head, > + struct ksm_stable_node *failing_node, > + struct ksm_stable_node **healthy_dupdup) > +{ > + struct ksm_stable_node *dup; > + struct hlist_node *hlist_safe; > + struct folio *healthy_folio; > + > + if (!is_stable_node_chain(chain_head) || !is_stable_node_dup(failing_node)) > + return NULL; > + > + hlist_for_each_entry_safe(dup, hlist_safe, &chain_head->hlist, hlist_dup) { > + if (dup == failing_node) > + continue; > + > + healthy_folio = ksm_get_folio(dup, KSM_GET_FOLIO_TRYLOCK); > + if (healthy_folio) { > + *healthy_dupdup = dup; > + return healthy_folio; > + } > + } > + > + return NULL; > +} > + > +static struct page *create_new_stable_node_dup(struct ksm_stable_node *chain_head, > + struct folio *healthy_folio, > + struct ksm_stable_node **new_stable_node) > +{ > + int nid; > + unsigned long kpfn; > + struct page *new_page = NULL; > + > + if (!is_stable_node_chain(chain_head)) > + return NULL; > + > + new_page = alloc_page(GFP_HIGHUSER_MOVABLE | __GFP_ZERO); > + if (!new_page) > + return NULL; > + > + copy_highpage(new_page, folio_page(healthy_folio, 0)); > + > + *new_stable_node = alloc_stable_node(); > + if (!*new_stable_node) { > + __free_page(new_page); > + return NULL; > + } > + > + INIT_HLIST_HEAD(&(*new_stable_node)->hlist); > + kpfn = page_to_pfn(new_page); > + (*new_stable_node)->kpfn = kpfn; > + nid = get_kpfn_nid(kpfn); > + DO_NUMA((*new_stable_node)->nid = nid); > + (*new_stable_node)->rmap_hlist_len = 0; > + > + (*new_stable_node)->head = STABLE_NODE_DUP_HEAD; > + hlist_add_head(&(*new_stable_node)->hlist_dup, &chain_head->hlist); > + ksm_stable_node_dups++; > + folio_set_stable_node(page_folio(new_page), *new_stable_node); > + folio_add_lru(page_folio(new_page)); There seems to be a lot of copy-paste. For example, why no reuse stable_node_chain_add_dup()? Or why not try to reuse stable_tree_insert() in the first place? Try to reuse or factor out instead of copy-pasting, please. > + > + return new_page; > +} > + > +static int replace_failing_page(struct vm_area_struct *vma, struct page *page, > + struct page *kpage, unsigned long addr) > +{ > + struct folio *kfolio = page_folio(kpage); > + struct mm_struct *mm = vma->vm_mm; > + struct folio *folio = page_folio(page); > + pmd_t *pmd; > + pte_t *ptep; > + pte_t newpte; > + spinlock_t *ptl; > + int err = -EFAULT; > + struct mmu_notifier_range range; > + > + pmd = mm_find_pmd(mm, addr); > + if (!pmd) > + goto out; > + > + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, addr, > + addr + PAGE_SIZE); > + mmu_notifier_invalidate_range_start(&range); > + > + ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); > + if (!ptep) > + goto out_mn; > + > + folio_get(kfolio); > + folio_add_anon_rmap_pte(kfolio, kpage, vma, addr, RMAP_NONE); > + newpte = mk_pte(kpage, vma->vm_page_prot); > + > + flush_cache_page(vma, addr, pte_pfn(ptep_get(ptep))); > + ptep_clear_flush(vma, addr, ptep); > + set_pte_at(mm, addr, ptep, newpte); > + > + folio_remove_rmap_pte(folio, page, vma); > + if (!folio_mapped(folio)) > + folio_free_swap(folio); > + folio_put(folio); > + > + pte_unmap_unlock(ptep, ptl); > + err = 0; > +out_mn: > + mmu_notifier_invalidate_range_end(&range); > +out: > + return err; > +} This is a lot of copy-paste from replace_page(). Isn't there a way to avoid this duplication by unifying both functions in some way? > + > +static void migrate_to_target_dup(struct ksm_stable_node *failing_node, > + struct folio *failing_folio, > + struct folio *target_folio, > + struct ksm_stable_node *target_dup) > +{ > + struct ksm_rmap_item *rmap_item; > + struct hlist_node *hlist_safe; > + int err; > + > + hlist_for_each_entry_safe(rmap_item, hlist_safe, &failing_node->hlist, hlist) { > + struct mm_struct *mm = rmap_item->mm; > + unsigned long addr = rmap_item->address & PAGE_MASK; Can be const. > + struct vm_area_struct *vma; > + > + if (!mmap_read_trylock(mm)) > + continue; > + > + if (ksm_test_exit(mm)) { > + mmap_read_unlock(mm); > + continue; > + } > + > + vma = vma_lookup(mm, addr); > + if (!vma) { > + mmap_read_unlock(mm); > + continue; > + } > + > + if (!folio_trylock(target_folio)) { Can't we leave the target folio locked the whole time? The caller already locked it, why not keep it locked until we're done? > + mmap_read_unlock(mm); > + continue; > + } > + > + err = replace_failing_page(vma, &failing_folio->page, > + folio_page(target_folio, 0), addr); > + if (!err) { > + hlist_del(&rmap_item->hlist); > + rmap_item->head = target_dup; > + hlist_add_head(&rmap_item->hlist, &target_dup->hlist); > + target_dup->rmap_hlist_len++; > + failing_node->rmap_hlist_len--; > + } > + > + folio_unlock(target_folio); > + mmap_read_unlock(mm); > + } > + > +} > + > +static bool ksm_recover_within_chain(struct ksm_stable_node *failing_node) > +{ > + struct folio *failing_folio = NULL; > + struct ksm_stable_node *healthy_dupdup = NULL; > + struct folio *healthy_folio = NULL; > + struct ksm_stable_node *chain_head = NULL; > + struct page *new_page = NULL; > + struct ksm_stable_node *new_stable_node = NULL; Only initialize what needs initialization (nothing in here?) and combine where possible. Like struct folio *failing_folio, *healthy_folio; > + > + if (!is_stable_node_dup(failing_node)) > + return false; > + > + guard(mutex)(&ksm_thread_mutex); > + failing_folio = ksm_get_folio(failing_node, KSM_GET_FOLIO_NOLOCK); > + if (!failing_folio) > + return false; > + > + chain_head = find_chain_head(failing_node); > + if (!chain_head) > + return NULL; > + > + healthy_folio = find_healthy_folio(chain_head, failing_node, &healthy_dupdup); > + if (!healthy_folio) { > + folio_put(failing_folio); > + return false; > + } > + > + new_page = create_new_stable_node_dup(chain_head, healthy_folio, &new_stable_node); Why are you returning a page here and not a folio? -- Cheers David / dhildenb