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large overhead in libmount

From: Pádraig Brady
Subject: large overhead in libmount
Date: Tue, 20 Jan 2015 02:01:13 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0

On 30/12/14 22:06, Bernhard Voelker wrote:
> I just pulled the recent gnulib update, and now the above, expensive
> test fails:
>    + ulimit -v 40000
>    + du -sh d
>    du: fts_read failed: d: Cannot allocate memory
>    + fail=1
> I guess this due to the inclusion of libmount?

Yes I get the same issue in that test:

Indeed there is significant overhead in using libmount as shown below.
This is a crazy amount of overhead just to read /proc/self/mountinfo,
and is the sort of creeping dependencies I hate.  The proposed solution
in the attached gnulib patch, is to require ./configure --with-libmount
to enable this feature. I.E. it's disabled by default.


======= without =========
$ (ulimit -v 5380; du -s .)

$ ldd /usr/bin/du
linux-vdso.so.1 =>  (0x00007fff0d7fe000)
libc.so.6 => /lib64/libc.so.6 (0x00007fd414a32000)
/lib64/ld-linux-x86-64.so.2 (0x00007fd414e0b000)

$ time du -s src/du.c >/dev/null
real    0m0.003s
user    0m0.000s
sys     0m0.003s

======= with =========
$ (ulimit -v 23250; src/du -s .)

$ ldd src/du
linux-vdso.so.1 =>  (0x00007fff76ca8000)
libc.so.6 => /lib64/libc.so.6 (0x00007f2a1f742000)
/lib64/ld-linux-x86-64.so.2 (0x00007f2a1fd61000)
 libmount.so.1 => /lib64/libmount.so.1 (0x00007f2a1faff000)
  libblkid.so.1 => /lib64/libblkid.so.1 (0x00007f2a1f501000)
  libuuid.so.1 => /lib64/libuuid.so.1 (0x00007f2a1f2fc000)
  libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f2a1f0d7000)
  libpcre.so.1 => /lib64/libpcre.so.1 (0x00007f2a1ee69000)
  liblzma.so.5 => /lib64/liblzma.so.5 (0x00007f2a1ec44000)
  libdl.so.2 => /lib64/libdl.so.2 (0x00007f2a1ea40000)
  libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f2a1e823000)

$ time src/du -s src/du.c >/dev/null
real    0m0.006s
user    0m0.001s
sys     0m0.005s

Attachment: gnulib-optional-libmount.patch
Description: Text Data

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