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s=MBO0001; t=1717687742; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=sHfJnp2lcftRA6X7UnUOG6z9rpZyMvNccJKHK19bpqc=; b=LvVi4t/Y+JebtJu90GV9FYjqoscL8pKkggLe38PrTSDSMZo9hdjB+mAopTSegccbb4HViK jEdpQvAPqv0A7OTxY4mJHxa6rIxV84WwV0Z0Kz8+c77WOI4b/YjHXJO7pMTyDXgQoObxrb kfEUhB4NgDvh5fMKFbExU1LpjV1b87HsQIWbi/wGc/F8Q/gK1zWqx1Cw/sdZSB1vDpgkrs JtQ3wmsLWQUAF6MnNzqPV6dHjyyT4gZgacEAUHge2VlAgCRZVCePmiNOfl7FpyTn7hDPAq zyUoQots/+9NRT8V/GupLseBbSqcC1xTzeGRznKZtgALr5NyjtIUzAiQCYW01w== Date: Thu, 6 Jun 2024 15:28:58 +0000 From: "Pankaj Raghav (Samsung)" To: Matthew Wilcox Cc: Shuah Khan , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, gost.dev@samsung.com, mcgrof@kernel.org, linux-kselftest@vger.kernel.org, Zi Yan , Pankaj Raghav Subject: Re: [PATCH] selftests/mm: use volatile keyword to not optimize mmap read variable Message-ID: <20240606152858.hmtnmieyesv7o5i3@quentin> References: <20240606135835.600022-1-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 8AE3E16000E X-Stat-Signature: hzuaw5ephc1gynx5gaioati8c3oaro7k X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1717687747-742780 X-HE-Meta: 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 tyPdqiuK fENzmh/5oI4O/x+Ve1Dj1d1WnMEGX7MGZyc9x9WLF5BMeGR/5TMDVqSHV0zb5jva/ABgiZT8t+s+NBC4FfeO8oc0KKvy2/12B+vdmdV9+XRhnJXaCxG9cL9h5utHMe1XxnO+kfLTUhD4cuHxeNlWuQuTgVn2oIqN0175QYE5yTJHuE9TpLurYAbxwi7K/d3ZoWwLT 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, Jun 06, 2024 at 03:35:31PM +0100, Matthew Wilcox wrote: > On Thu, Jun 06, 2024 at 01:58:35PM +0000, Pankaj Raghav (Samsung) wrote: > > +++ b/tools/testing/selftests/mm/split_huge_page_test.c > > @@ -300,7 +300,7 @@ int create_pagecache_thp_and_fd(const char *testfile, size_t fd_size, int *fd, > > char **addr) > > { > > size_t i; > > - int __attribute__((unused)) dummy = 0; > > + volatile int __attribute__((unused)) dummy = 0; > > The mistake made by whoever wrote this test was making 'dummy' a stack > variable. That lets the compiler figure out that it's unused. If you > make it a top-level variable (not static) so the compiler can't tell > whether it's referenced by a different compilation unit, it can't make > that deduction. And you don't need the stupid attibute or volatile on it. I did cringe a little before adding the volatile keyword. While not a fan of global variables, that might be better than all these keywords. I will send a v2 right away! Thanks. -- Pankaj