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 EBDD63F6C4B for ; Tue, 9 Jun 2026 09:18:37 +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=1780996719; cv=none; b=CLAAcTEu69DUvD0l1+k9GUzwTXhUnjZw++aeLn4fIiuJ/FIyJjPZjcAfBMBxUmLdymK/RTt+SU54rXGjUncuR1NN8p6PL5k2YANblg/jne9fK4Niq5fQIE2FGkhW8Ugy2G9Es2ubc58eJwi/V5ddqJoM+ubvvdnJYTKIklBxLv4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780996719; c=relaxed/simple; bh=PRuaveGo4UqbilWh0HaES9qTtI925aUXX8vVPwom/lQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dnliXV4eu3ynMrM8lQQt5wokaRhsQQdlF0cTVpNSKlEvqCPQznXrtKTOzGQA0OjNy+XPLH0NKdTmmPNxYIPF3KnIiV6c1AuNvnTMKKnSdsirZ5hmpgg4dDEdoXPW7ze2TKcjH1+b6p07rhpR0Q60dD5TycbxN7pi6YaviitBd/A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J/YeKi2s; 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="J/YeKi2s" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D18D91F00893; Tue, 9 Jun 2026 09:18:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780996717; bh=YzacP3ypYf5fRrXAJ98V9+ticq2bZRWt9AFGg5i34QY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=J/YeKi2s/52CbzahjMsaAoNojqTOr85R14eTi47hgVOJrYPk/aOzeBPSWP/FH4qdP 614Gruk0mJTut2Nf2FKhtaBEuRwDiGU95zUD9qsUSAp+8Jmsc8MTkOVNQY2a6eMwnb 5Yg8rsDhM1NIKxF6t4rR2YeXlrpIeYVrvL24XRKoC7aFhkIJymeaPD0ReKb/58ZXkb lO6FictpCQ70T5ZAEZExH5DhnG/XtAW9h0FqrcIKm94BmM1pe13NEYJd6BMKlNTSAO deoWNXuUSs+PwU87kV0U3QyGmgsiOnfOcJvd7ZWOexx7cRFqnQRFlgoZoIcPhUX9wz cQrRGeJY359nw== Message-ID: Date: Tue, 9 Jun 2026 11:18:34 +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 v8 3/3] ksm: add mremap selftests for ksm_rmap_walk To: xu.xin16@zte.com.cn, akpm@linux-foundation.org Cc: chengming.zhou@linux.dev, hughd@google.com, wang.yaxin@zte.com.cn, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ljs@kernel.org References: <20260609124746153K8Y8tYI_4pNVKogGMdglR@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 6/9/26 06:47, 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. > > We add the calling of mremap() and then trigger KSM to merge pages before > migrating, which is specifically to test an optimization which is > introduced by this patch ("ksm: Optimize rmap_walk_ksm by passing a > suitable address pgoff"). > > 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 | 86 +++++++++++++++++++++++++++++++ > 1 file changed, 86 insertions(+) > > diff --git a/tools/testing/selftests/mm/rmap.c b/tools/testing/selftests/mm/rmap.c > index 53f2058b0ef2..1cdc4beb48c2 100644 > --- a/tools/testing/selftests/mm/rmap.c > +++ b/tools/testing/selftests/mm/rmap.c > @@ -430,4 +430,90 @@ TEST_F(migrate, ksm) > propagate_children(_metadata, data); > } > > +static void prepare_pages(struct global_data *data, int nr_pages) > +{ > + /* Allocate exactly pages for the test */ > + data->mapsize = nr_pages * 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 all 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; > + void *old_region; > + void *new_region; > + int nr_pages = 32; Likely you should do const unsigned int nr_pages = 16; and then simply multiply it by 2 for the temporary larger mmap. > + long merging_pages; > + > + prepare_pages(data, nr_pages); Is it really worth moving that into a helper function? > + > + if (ksm_start() < 0) > + return FAIL_ON_CHECK; Why the merge here? Wouldn't we want to merge after mremap()? mremap() will just unshare either way? > + > + old_region = data->region; > + /* > + * Mremap the second half region to the first half location (FIXED). > + */ Okay, so we create a VMA and populated anonymous pages. Might be from THPs, do we care? I guess due to the split-on-dedup, this should be ok. Now we mremap half of it over the other half. > + new_region = mremap(old_region + data->mapsize / 2, data->mapsize / 2, > + data->mapsize / 2, MREMAP_MAYMOVE | MREMAP_FIXED, > + old_region); > + if (new_region == MAP_FAILED) { > + ksft_print_msg("mremap failed: %s\n", strerror(errno)); > + return FAIL_ON_CHECK; > + } > + data->region = new_region; > + data->mapsize /= 2; /* mapping is now half of original */ Let's avoid the use of trailing comments where possible. > + > + if (ksm_start() < 0) > + return FAIL_ON_CHECK; > + > + /* Attempt to migrate the merged KSM page */ > + ret = try_to_move_page(data->region); > + if (ret != 0) { > + ksft_print_msg("migration of KSM page after mremap failed\n"); > + return FAIL_ON_CHECK; > + } > + > + /* Ensure ksmd scan two turns at least to update ksm counters */ > + if (ksm_start() < 0) > + return FAIL_ON_CHECK; Why do we have to re-run KSM? ksm_start() already performed two runs. To remove any leftover rmap entries? But fundamentally, wouldn't it better to query before+after the try_to_move_page() the PFN of all pages, to (a) make sure that they are the same before (all merged, if not -> skip) and (b) make sure that all were migrated (if still old PFN -> not migrated -> BUG). > + > + merging_pages = ksm_get_self_merging_pages(); > + printf("merging_pages:%ld\n", merging_pages); > + if (merging_pages != nr_pages / 2) { [...] > +TEST_F(migrate, ksm_and_mremap) > +{ > + struct global_data *data = &self->data; > + int ret; > + > + /* Skip if KSM is not available */ > + if (ksm_stop() < 0) > + SKIP(return, "accessing \"/sys/kernel/mm/ksm/run\" failed"); > + if (ksm_get_full_scans() < 0) > + SKIP(return, "accessing \"/sys/kernel/mm/ksm/full_scan\" failed"); > + > + ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0); > + if (ret < 0 && errno == EINVAL) > + SKIP(return, "PR_SET_MEMORY_MERGE not supported"); > + else if (ret) > + ksft_exit_fail_perror("PR_SET_MEMORY_MERGE=1 failed"); Why are we not simply using MADV_MERGEABLE instead of the prctl? -- Cheers, David