From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: ext4 extent status tree LRU locking Date: Mon, 17 Jun 2013 22:47:27 -0400 Message-ID: <20130618024727.GA24479@thunk.org> References: <51B7B128.60909@intel.com> <20130614140940.GA20401@gmail.com> <20130614140215.GA1017@thunk.org> <20130614170028.GA21544@gmail.com> <20130614180054.GB1017@thunk.org> <20130617101033.GA17828@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: Dave Hansen , linux-ext4@vger.kernel.org, LKML , Jan kara Return-path: Content-Disposition: inline In-Reply-To: <20130617101033.GA17828@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org > Subject: [PATCH v2] ext4: improve extent cache shrink mechanism to avoid to burn CPU time > > From: Zheng Liu > > Now we maintain an proper in-order LRU list in ext4 to reclaim entries > from extent status tree when we are under heavy memory pressure. For > keeping this order, a spin lock is used to protect this list. But this > lock burns a lot of CPU time. We can use the following steps to trigger > it. > > % cd /dev/shm > % dd if=/dev/zero of=ext4-img bs=1M count=2k > % mkfs.ext4 ext4-img > % mount -t ext4 -o loop ext4-img /mnt > % cd /mnt > % for ((i=0;i<160;i++)); do truncate -s 64g $i; done > % for ((i=0;i<160;i++)); do cp $i /dev/null &; done > % perf record -a -g > % perf report > > This commit tries to fix this problem. Now a new member called > i_touch_when is added into ext4_inode_info to record the last access > time for an inode. Meanwhile we never need to keep a proper in-order > LRU list. So this can avoid to burns some CPU time. When we try to > reclaim some entries from extent status tree, we use list_sort() to get > a proper in-order list. Then we traverse this list to discard some > entries. In ext4_sb_info, we use s_es_last_sorted to record the last > time of sorting this list. When we traverse the list, we skip the inode > that is newer than this time, and move this inode to the tail of LRU > list. When the head of the list is newer than s_es_last_sorted, we will > sort the LRU list again. > > In this commit, we break the loop if s_extent_cache_cnt == 0 because > that means that all extents in extent status tree have been reclaimed. > > Meanwhile in this commit, ext4_es_{un}register_shrinker()'s prototype is > changed to save a local variable in these functions. > > Reported-by: Dave Hansen > Cc: "Theodore Ts'o" > Signed-off-by: Zheng Liu Applied, thanks. - Ted