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b=dA9P810z7x1JH1ynoG6lOwf84Mb0bqTX9/ie1bX0VDXMx7xGoKjtIrkaaccrMHuyD ydhlM37CTf1GCeYUe7zMDcylp6K0Gy9R1u8o+57GkLWmPyoBKt0TVK85sv9dGtFYba R/KOoNGFpbBIfNv1w4WxhddVxVEWkLA5imbDhurLp+/Eo1cvqYazCZsoqW0hJLjN3y QzEjnHu8wqz+zqJvf/zSgL0he6HfTRt3w7rka72w8zxFtPMNTWvhcQHOJFl3WkRH3d iQbJEUGDEn2vA6TTU7cALEUIagm6gVR8ItP8ypktR4IHYWywINWbBW883fdEnxJjwM mspMSgXwzV70w== Message-ID: <24cdec9c-28b5-4e44-bb05-fef27ef09846@kernel.org> Date: Mon, 24 Aug 2026 12:33:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] selftests/mm: disable smart scan for ksm_tests To: Zenghui Yu , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Cc: akpm@linux-foundation.org, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, shr@devkernel.io, ljs@kernel.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org References: <20260823184314.45044-1-zenghui.yu@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5CB5280005 X-Stat-Signature: 1monwxdw78qwjhr8wxkg93ph1iksup3r X-Rspam-User: X-HE-Tag: 1787567597-449628 X-HE-Meta: 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 g61TH8C7 sXoCyvwmhNGL19ltkxBA4xV1i0kbnjWWOn3NjPK9BRwyJVDmz9WcbPv7vD6au2d5fTohWHd198Sw1+ITTXVqVq7Fk5yX2c7bZ9y0ZZ79D/b1h0BjZhBjnM2iJjqWOPT3gbawaYOFZd9xjVHiXW/AIRE5nKByfP/yWZL3dCq+9NJdS28b5xi7Q8zui4E9hh/k4ASYDG6jTKbK/GmkTnE59hSeeWggKQrlFjNa0oicurKPDkQEuaPmAsYYZ46e4vR0pC6xoC2HegVo9TPBh3TIYRRcRI0R/IzeChQlBXqSJ5QpxBGjusFkwhZGreQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/23/26 20:43, Zenghui Yu wrote: > From: "Zenghui Yu (Huawei)" > > The "KSM NUMA merging" test allocates two identical pages on two NUMA nodes > and verifies KSM will merge these two pages after 2 scans (see > ksm_merge_pages()). But when smart scan is enabled, pages that have > previously not been de-duplicated may get skipped for some scans. Verifying > KSM behavior after only 2 scans may not be enough. > > $ ./ksm_tests -N -d > TAP version 13 > 1..1 > pages_shared : 0 > pages_sharing : 0 > max_page_sharing : 256 > full_scans : 211 > pages_unshared : 1 > pages_volatile : 2 > stable_node_chains: 0 > stable_node_dups : 0 > general_profit : -128 > ksm_rmap_items 2 > ksm_zero_pages 0 > ksm_merging_pages 0 > ksm_process_profit -128 > ksm_merge_any: no > ksm_mergeable: yes > not ok 1 KSM NUMA merging > # Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0 How did you reproduce this? Is this an actual test result? ~/linux/tools/testing/selftests/mm$ cat /sys/kernel/mm/ksm/smart_scan 1 ~/linux/tools/testing/selftests/mm$ sudo ./ksm_tests -N -d TAP version 13 1..1 pages_shared : 1 pages_sharing : 1 max_page_sharing : 256 full_scans : 1283 pages_unshared : 0 pages_volatile : 0 stable_node_chains: 0 stable_node_dups : 0 general_profit : 3968 ksm_rmap_items 2 ksm_zero_pages 0 ksm_merging_pages 2 ksm_process_profit 8064 ksm_merge_any: no ksm_mergeable: yes ok 1 KSM NUMA merging # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 > > This specific test fails because KSM started scanning the second page > whilst the first page had already been scanned for 16 times How is that supposed to happen? The sequence we have is: numa1_map_ptr = numa_alloc_onnode(page_size, first_node); numa2_map_ptr = numa_alloc_onnode(page_size, second_node); ... memset(numa1_map_ptr, '*', page_size); memset(numa2_map_ptr, '*', page_size); ... if (ksm_merge_pages(merge_type, numa1_map_ptr, page_size, start_time, timeout) ... KSM smart scan operates on rmap entries. rmap entries are per MM. -- Cheers, David