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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id d205sm1775689qkg.66.2019.03.20.15.12.41 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 Mar 2019 15:12:41 -0700 (PDT) Subject: Re: [RESEND#2 PATCH] mm/compaction: fix an undefined behaviour To: Andrew Morton Cc: mgorman@techsingularity.net, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190320203338.53367-1-cai@lca.pw> <20190320145826.9c647fe53bd999bbd2ee188d@linux-foundation.org> From: Qian Cai Message-ID: Date: Wed, 20 Mar 2019 18:12:40 -0400 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.3.3 MIME-Version: 1.0 In-Reply-To: <20190320145826.9c647fe53bd999bbd2ee188d@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: On 3/20/19 5:58 PM, Andrew Morton wrote: >> --- >> mm/compaction.c | 4 +++- >> 1 file changed, 3 insertions(+), 1 deletion(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index e1a08fc92353..0d1156578114 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1157,7 +1157,9 @@ static bool suitable_migration_target(struct compact_control *cc, >> static inline unsigned int >> freelist_scan_limit(struct compact_control *cc) >> { >> - return (COMPACT_CLUSTER_MAX >> cc->fast_search_fail) + 1; >> + return (COMPACT_CLUSTER_MAX >> >> + min((unsigned short)(BITS_PER_LONG - 1), cc->fast_search_fail)) >> + + 1; >> } > > That's rather an eyesore. How about > > static inline unsigned int > freelist_scan_limit(struct compact_control *cc) > { > unsigned short shift = BITS_PER_LONG - 1; > > return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1; > } Agree. It looks better.