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h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=nWCE2ohU0p5JfW06/Z6E8d6Ezt4RMf1Y7XdlACppk1QWxGvyts1ndltbyeYQu8gJo hIL/OPYc3jTeB5LDlYc5NShzW29jHIQ2ZI2wHYwHsFDfyzOVpIfaexxO65T2w7JYXv Hx5bKG6I5WZk4V1iij+5PkKR9q2ey9K89F6U13B4= Date: Fri, 7 Jun 2024 21:39:36 -0700 From: Andrew Morton To: "Pankaj Raghav (Samsung)" Cc: Shuah Khan , linux-mm@kvack.org, gost.dev@samsung.com, David Hildenbrand , willy@infradead.org, mcgrof@kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Zi Yan , Pankaj Raghav Subject: Re: [PATCH v3] selftests/mm: use asm volatile to not optimize mmap read variable Message-Id: <20240607213936.a58028617aacdbf6913d3735@linux-foundation.org> In-Reply-To: <20240606203619.677276-1-kernel@pankajraghav.com> References: <20240606203619.677276-1-kernel@pankajraghav.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 11F5118000A X-Stat-Signature: 7334yyzs7s1x8kig9qus56n3pd3u1ysp X-HE-Tag: 1717821578-422066 X-HE-Meta: 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 vIE2NxBf LX4FTeao1AQAp9AbrZDGplsWnGSIxPeBsylwEvKl2SE4NKlodfzkgK8TCWPL3fLeK5bW60TA1RMQiyo/I3Mt4O6IK8jszjmOjmxw0aQqIfk0GmtDpgBXhfpi6LexU9ERqH6pg2CN2XQwM07KtF9wNV7TZfk+PbgKMYd7qBK96wNcMmfOhbpZ8eKNj+2yBcFRrk61To9S5qeA3q0sqdITq07IZ452ydGZuAerVd++l0O4hWb0Z96a+xIX+VSRt8PekrhXoz70ehgkfYsD/lVKM+xKbQRtbbhFTBHBijembIPxa34KgVl1zC2Fbxw== 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 Thu, 6 Jun 2024 20:36:19 +0000 "Pankaj Raghav (Samsung)" wrote: > From: Pankaj Raghav > > create_pagecache_thp_and_fd() in split_huge_page_test.c used the > variable dummy to perform mmap read. > > However, this test was skipped even on XFS which has large folio > support. The issue was compiler (gcc 13.2.0) was optimizing out the > dummy variable, therefore, not creating huge page in the page cache. > > Use asm volatile() trick to force the compiler not to optimize out > the loop where we read from the mmaped addr. This is similar to what is > being done in other tests (cow.c, etc) > > As the variable is now used in the asm statement, remove the unused > attribute. > What are the runtime effects of this change? An inappropriate test failure? If so, shouldn't we fix 6.9.x kernels also? And is fc4d182316bd ("mm: huge_memory: enable debugfs to split huge pages to any order") an appropriate Fixes: target?