From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 3BCCE3FF8AF for ; Wed, 13 May 2026 12:10:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778674231; cv=none; b=OlMCQWl1NT3m2Bj6hTjnGmFgu6SHWXOLC3qx6OkFyk/VFAjKh6WqBZLT1+N34ZaUznrm9twr6KrRGhn8TGta3TXRUvdwzgjTESa+5KVzC+Dm/zN12wQd3pv/oqnLPII9VgGGDxLtPRZruvGGF68cF3Gteyr2LK2Vx2boJnKTgZ0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778674231; c=relaxed/simple; bh=DKsaSfcfuE1IVUrZuwxuOKUdV2c4V7dwWzUcqfRcakg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PRD/DS44Lh7cE5TLZkig+pQgLKVF0MzwsCh0pO7msQG1np7qvTEQu7XLvBNF7E7fZ3rNUi3F8gXiTG/9SVTEAv6wlTxrDqLo2yVvjKtf2sgSqTw2GLAACFH2qOgcOqT00IUtlYX93jH7JhbZCRjiq1dkpXhLETkw1PwS/VicHCc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QWGtMWLa; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QWGtMWLa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 80B42C2BCB7; Wed, 13 May 2026 12:10:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778674230; bh=DKsaSfcfuE1IVUrZuwxuOKUdV2c4V7dwWzUcqfRcakg=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=QWGtMWLaBDi9QplgclFyV9E7EYmvm2m2mtJk+Q2QlJgCMFc6T0CBreB+g1kFIN1jB h9Dvmb9bAuE1t+CGkTs/AXddm5G+oG/BRz4oGwD3wOUr+KMcUZ4zgjMpktA1HzrJ/O 9FCU/X/OfkyKdTufMokoPzxPigrEnx1K8AYKltZnRt7lKf6olDPGZU1f0FnJ/TR33C saSQEbmmDHNtaJhqIC+f++57hEezrT4l5zhorNpJF3p5ppddWXnyaKekhfFOzt7VS2 ceJLkQxmxwxG8xuEeBK4/7u0mv7bLVhlPv75hAGRJDnmS1nJMPW94tCkteIWdmEx7z i02HiNcB+sucQ== Message-ID: <962c2a3d-0502-44b9-a115-863b513bafe2@kernel.org> Date: Wed, 13 May 2026 14:10:26 +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 v4 5/5] ksm: add mremap selftests for ksm_rmap_walk To: xu.xin16@zte.com.cn, ljs@kernel.org, akpm@linux-foundation.org Cc: hughd@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, michel@lespinasse.org References: <20260503205153715oK1yza2bba5lfAl3QwiPx@zte.com.cn> 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 5/3/26 14:51, xu.xin16@zte.com.cn wrote: > From: xu xin > The existing tools/testing/selftests/mm/rmap.c has already one testcase > for ksm_rmap_walk in TEST_F(migrate, ksm), which takes use of migration > of page from one NUMA node to another NUMA node. However, it just lacks > the scenario of mremapped VMAs. > > There are one worker process and several checker processes, and in worker, > we add the calling of mremap() and then trigger KSM to merge pages before > migrating, , which is specailly to test a optimization which is introduced > by this patch ("ksm: Optimize rmap_walk_ksm by passing a suitable address > range"). In other checker processes, we just trigger KSM to merge pages > from each child process and check their PFN. > > This test can reproduce the issue that Hugh points out at > https://lore.kernel.org/all/02e1b8df-d568-8cbb-b8f6-46d5476d9d75@google.com/ > > Signed-off-by: xu xin > --- > tools/testing/selftests/mm/rmap.c | 79 ++++++++++++++++++++++++++++ > tools/testing/selftests/mm/vm_util.c | 38 +++++++++++++ > tools/testing/selftests/mm/vm_util.h | 2 + > 3 files changed, 119 insertions(+) > > diff --git a/tools/testing/selftests/mm/rmap.c b/tools/testing/selftests/mm/rmap.c > index 53f2058b0ef2..fced1f6304ac 100644 > --- a/tools/testing/selftests/mm/rmap.c > +++ b/tools/testing/selftests/mm/rmap.c > @@ -430,4 +430,83 @@ TEST_F(migrate, ksm) > propagate_children(_metadata, data); > } > > +static void prepare_two_pages(struct global_data *data) > +{ > + /* Allocate exactly 2 pages for the test */ > + data->mapsize = 2 * getpagesize(); > + data->region = mmap(NULL, data->mapsize, PROT_READ | PROT_WRITE, > + MAP_PRIVATE | MAP_ANON, -1, 0); > + if (data->region == MAP_FAILED) > + ksft_exit_fail_perror("mmap failed"); > + > + /* Fill both pages with identical content to encourage KSM merging */ > + memset(data->region, 0x77, data->mapsize); > +} > + > +static int mremap_merge_and_migrate(struct global_data *data) > +{ > + int ret, pagemap_fd; > + void *old_region = data->region; > + unsigned long page_sz = getpagesize(); > + > + /* > + * Mremap the second page to the first page's location (FIXED). > + * This effectively overwrites the first page, leaving the second page > + * unmapped. The physical page originally at the second page is now > + * mapped at the first page's virtual address. > + */ But if there is only a single page, why should it get merged by KSM? -- Cheers, David