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Date:   Wed, 19 Aug 2020 00:24:38 -0400
From:   "Theodore Y. Ts'o" <tytso@mit.edu>
To:     brookxu <brookxu.cn@gmail.com>
Cc:     adilger.kernel@dilger.ca, riteshh@linux.ibm.com, jack@suse.cz,
        linux-ext4@vger.kernel.org
Subject: Re: [PATCH v5 2/2] ext4: limit the length of per-inode prealloc list
Message-ID: <20200819042438.GF162457@mit.edu>
References: <d7a98178-056b-6db5-6bce-4ead23f4a257@gmail.com>
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On Mon, Aug 17, 2020 at 03:36:15PM +0800, brookxu wrote:
> In the scenario of writing sparse files, the per-inode prealloc list may
> be very long, resulting in high overhead for ext4_mb_use_preallocated().
> To circumvent this problem, we limit the maximum length of per-inode
> prealloc list to 512 and allow users to modify it.
> 
> After patching, we observed that the sys ratio of cpu has dropped, and
> the system throughput has increased significantly. We created a process
> to write the sparse file, and the running time of the process on the
> fixed kernel was significantly reduced, as follows:
> 
> Running time on unfixed kernel：
> [root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
> real    0m2.051s
> user    0m0.008s
> sys     0m2.026s
> 
> Running time on fixed kernel：
> [root@TENCENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
> real    0m0.471s
> user    0m0.004s
> sys     0m0.395s

Thanks, applied with Ritesh's suggested spelling fix up.

		     	      			 - Ted