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Tue, 05 Aug 2025 10:03:54 -0700 (PDT) Date: Tue, 5 Aug 2025 17:03:53 +0000 From: Wei Yang To: Donet Tom Cc: Wei Yang , Aboorva Devarajan , akpm@linux-foundation.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, shuah@kernel.org, pfalcato@suse.de, david@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, ritesh.list@gmail.com Subject: Re: [PATCH v3 3/7] selftest/mm: Fix ksm_funtional_test failures Message-ID: <20250805170353.6vlbyg6qn5hv4yzz@master> Reply-To: Wei Yang References: <20250729053403.1071807-1-aboorvad@linux.ibm.com> <20250729053403.1071807-4-aboorvad@linux.ibm.com> <20250804091141.ifwryfmgjepwrog4@master> <20fb853c-7d79-4d26-9c8a-f6ce9367d424@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20fb853c-7d79-4d26-9c8a-f6ce9367d424@linux.ibm.com> User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A8A7E20018 X-Stat-Signature: 61krzfwknmnp8domsn6syyh7nwg67bmm X-Rspam-User: X-HE-Tag: 1754413437-744299 X-HE-Meta: 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 ljlH+v/T 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Aug 05, 2025 at 11:39:15AM +0530, Donet Tom wrote: > >On 8/4/25 2:41 PM, Wei Yang wrote: >> On Tue, Jul 29, 2025 at 11:03:59AM +0530, Aboorva Devarajan wrote: >> > From: Donet Tom >> > [...] >> > diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c >> > index d8bd1911dfc0..996dc6645570 100644 >> > --- a/tools/testing/selftests/mm/ksm_functional_tests.c >> > +++ b/tools/testing/selftests/mm/ksm_functional_tests.c >> > @@ -46,6 +46,8 @@ static int ksm_use_zero_pages_fd; >> > static int pagemap_fd; >> > static size_t pagesize; >> > >> > +static void init_global_file_handles(void); >> > + >> > static bool range_maps_duplicates(char *addr, unsigned long size) >> > { >> > unsigned long offs_a, offs_b, pfn_a, pfn_b; >> > @@ -274,6 +276,7 @@ static void test_unmerge(void) >> > ksft_test_result(!range_maps_duplicates(map, size), >> > "Pages were unmerged\n"); >> > unmap: >> > + ksm_unmerge(); >> In __mmap_and_merge_range(), we call ksm_unmerge(). Why this one not help? >> >> Not very familiar with ksm stuff. Would you mind giving more on how this fix >> the failure you see? > > >The issue I was facing here was test_prctl_fork was failing. > ># [RUN] test_prctl_fork ># Still pages merged ># > >This issue occurred because the previous test performed a merge, causing >the value of /proc/self/ksm_merging_pages to reflect the number of >deduplicated pages. After that, a fork() was called. Post-fork, the child >process >inherited the parent's ksm_merging_pages value. > Yes, this one is fixed by calling init_global_file_handles() in child. >Then, the child process invoked __mmap_and_merge_range(), which resulted >in unmerging the pages and resetting the value. However, since the parent >process >had performed the merge, its ksm_merging_pages value also got reset to 0. >Meanwhile, the child process had not performed any merge itself, so the >inherited I assume the behavior described here is after the change to call init_global_file_handles() in child. Child process inherit the ksm_merging_pages from parent, which is reasonable to me. But I am confused why ksm_unmerge() would just reset ksm_merging_pages for parent and leave ksm_merging_pages in child process unchanged. ksm_unmerge() writes to /sys/kernel/mm/ksm/run, which is a system wide sysfs interface. I expect it applies to both parent and child. >value remained unchanged. That’s why get_my_merging_page() in the child was >returning a non-zero value. > I guess you mean the get_my_merging_page() in __mmap_and_merge_range() return a non-zero value. But there is ksm_unmerge() before it. Why this ksm_unmerge() couldn't reset the value, but a ksm_unmerge() in parent could. >Initially, I fixed the issue by calling ksm_unmerge() before the fork(), and >that >resolved the problem. Later, I decided it would be cleaner to move the >ksm_unmerge() call to the test cleanup phase. > Also all the tests before test_prctl_fork(), except test_prctl(), calls ksft_test_result(!range_maps_duplicates()); If the previous tests succeed, it means there is no duplicate pages. This means ksm_merging_pages should be 0 before test_prctl_fork() if other tests pass. And the child process would inherit a 0 ksm_merging_pages. (A quick test proves it.) So which part of the story I missed? -- Wei Yang Help you, Help me