linux-ext4 - Why deleting large files took so long?

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Message-ID: <CALQm4jiYtxKmfji9p2QPZ6vnXApQmGh8UVjtm2DWr94JF4B8yg@mail.gmail.com>
Date:	Wed, 7 Aug 2013 00:45:53 -0700
From:	Cuong Tran <cuonghuutran@...il.com>
To:	linux-ext4@...r.kernel.org
Subject: Why deleting large files took so long?

My apology if this is not the correct forum for this question. I am
trying to understand why deleting large files take so long? If this is
not the correct forum, please kindly let me know which forum I can ask
this question.

I created 4 large files, 30 GB per file, for total size of 120 GB.
Then when my machine was idle (no CPU, no IO), I deleted these 4 files
at the same time.

Deleting these files at the same time took 12 secs, most of each was
due to kernel time!

$  time rm -f large* test.log
real    0m12.002s
user    0m0.001s
sys     0m11.928s

Kernel is RedHat Enterprise 6.x
Linux ctran-ld 2.6.32-131.4.1.el6.x86_64 #1 SMP Fri Jun 10 10:54:26
EDT 2011 x86_64 x86_64 x86_64 GNU/Linux

Server has 64 GByte memory. Drive is SAS 15K RPM. CPU is Xeon
E5620@...0Hz, 8 cores including hyper-threading.

Why does it take so long to delete these files (diskIO during deleting
is about couple of 100 MBytes, probably to commit changes in meta-data
in journal).

Thanks so much for shedding light on this puzzle.

Cheers,

--Cuong
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