From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0DDC93E6DFA; Mon, 24 Aug 2026 10:33:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787567597; cv=none; b=kyGNQnrLqKJnKRwC1AYg1B/yf7J68G/QsDE0zOPTIMQiKcfGzjl3Fl3SrP1XUFBhQI7CdMNtsLfKX9spdvI45NW8V8dRnPJNOdqNf2qjWJJVYZLQCY0R0zpORr5RBR39Jte2lpN3xMqmf8LTYJ8G5U94MSgnAeojjITqUi/u96U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787567597; c=relaxed/simple; bh=eeZlz1K5E5SjfFMptNhNFsnUvxTL34d0HtdFkqU4MEs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Mtoj7A4Xr7KAHu+pCy0cYD2XWluxJgDPMlWuGf7nzYLLEXl5/vw8bwfEWFzwMZn4ZcqQVqvKJ8eXK5dRuBR4CfbWPGyPDa2ahHaW4uiRYcFYz5GlxHWov0sqQi5/eSEIDKvMqP3FAaZjZl2jjiapbt/ntd83Cfk40GXhy4nMwHI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dA9P810z; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dA9P810z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ACF9C1F000E9; Mon, 24 Aug 2026 10:33:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787567595; bh=Bg71OX1b/jhiRpPtjWiE4T7Rr7gYxguTgtyPDfmDXSM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 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] 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 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