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([2620:10d:c091:480::4da]) by smtp.gmail.com with ESMTPSA id x41sm217155qtj.52.2020.02.12.06.13.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Feb 2020 06:13:07 -0800 (PST) Subject: Re: [PATCH] mm: Don't bother dropping mmap_sem for zero size readahead To: Jan Kara , Andrew Morton Cc: linux-mm@kvack.org, Robert Stupp , Minchan Kim References: <20200212101356.30759-1-jack@suse.cz> From: Josef Bacik Message-ID: <46c80ca4-1e54-576a-a9e9-7bd8179df102@toxicpanda.com> Date: Wed, 12 Feb 2020 09:13:06 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200212101356.30759-1-jack@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed 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 2/12/20 5:13 AM, Jan Kara wrote: > When handling a page fault, we drop mmap_sem to start async readahead so > that we don't block on IO submission with mmap_sem held. However > there's no point to drop mmap_sem in case readahead is disabled. Handle > that case to avoid pointless dropping of mmap_sem and retrying the > fault. This was actually reported to block mlockall(MCL_CURRENT) > indefinitely. > > Fixes: 6b4c9f446981 ("filemap: drop the mmap_sem for all blocking operations") > Reported-by: Minchan Kim > Reported-by: Robert Stupp > Signed-off-by: Jan Kara Reviewed-by: Josef Bacik Thanks, Josef