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Tue, 8 Sep 2026 17:34:09 -0400 (EDT) Date: Tue, 8 Sep 2026 22:34:08 +0100 From: Kiryl Shutsemau To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, rppt@kernel.org Cc: linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, usama.anjum@arm.com, usama.arif@linux.dev, baolin.wang@linux.alibaba.com, nico.pache@linux.dev, ziy@nvidia.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, vbabka@kernel.org, agordeev@linux.ibm.com, jgg@ziepe.ca, leon@kernel.org, kernel-team@meta.com Subject: Re: [PATCH v5 16/19] selftests/mm: add khugepaged race harness Message-ID: References: <20260908125105.1510704-1-kirill@shutemov.name> <20260908125105.1510704-17-kirill@shutemov.name> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260908125105.1510704-17-kirill@shutemov.name> On Tue, Sep 08, 2026 at 01:51:02PM +0100, Kiryl Shutsemau wrote: > +static void *mremapper_fn(void *arg) > +{ > + unsigned int seed = (unsigned long)arg; > + > + while (!stop) { > + void *p; > + > + p = mremap(mremap_area, hpage_pmd_size, hpage_pmd_size, > + MREMAP_MAYMOVE | MREMAP_FIXED, mremap_scratch); > + if (p == MAP_FAILED) > + ksft_exit_fail_perror("mremap() away"); > + for (int i = 0; i < 8; i++) > + mremap_scratch[(rand_r(&seed) % > + (hpage_pmd_size / page_size)) * page_size] = 1; > + p = mremap(mremap_scratch, hpage_pmd_size, hpage_pmd_size, > + MREMAP_MAYMOVE | MREMAP_FIXED, mremap_area); > + if (p == MAP_FAILED) > + ksft_exit_fail_perror("mremap() back"); > + usleep(rand_r(&seed) % 2000); > + } > + return NULL; > +} Sashiko pointed out that mremap() freed scratch area and it has to be re-reserved for next cycle. Here's fixup: diff --git a/tools/testing/selftests/mm/khugepaged_race.c b/tools/testing/selftests/mm/khugepaged_race.c index c3478b5123e2..ccfe655b3ddd 100644 --- a/tools/testing/selftests/mm/khugepaged_race.c +++ b/tools/testing/selftests/mm/khugepaged_race.c @@ -209,6 +209,11 @@ static void *mremapper_fn(void *arg) MREMAP_MAYMOVE | MREMAP_FIXED, mremap_area); if (p == MAP_FAILED) ksft_exit_fail_perror("mremap() back"); + /* The move back unmapped the scratch address: claim it again */ + if (mmap(mremap_scratch, hpage_pmd_size, PROT_NONE, + MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE, + -1, 0) != (void *)mremap_scratch) + ksft_exit_fail_perror("mmap() mremap scratch"); usleep(rand_r(&seed) % 2000); } return NULL; -- Kiryl Shutsemau / Kirill A. Shutemov