[PATCH 0/2][SRU][E] improve ext4 performance with revert of a reverted ext4 fix

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/1846486

== SRU Justification Eoan ==

Now that 5.4 contains a fix to the bootup regression due to the
lack of entropy at bootable we should apply this fix and also
revert the revert of commit 
"Revert "ext4: make __ext4_get_inode_loc plug"".

== Fix ==

So, to clarify, apply the two upstream 5.4-rc commits:

commit 50ee7529ec4500c88f8664560770a7a1b65db72b
Author: Linus Torvalds <torvalds at linux-foundation.org>
Date: Sat Sep 28 16:53:52 2019 -0700

    random: try to actively add entropy rather than passively wait for it

commit 02f03c4206c1b2a7451d3b3546f86c9c783eac13
Author: Linus Torvalds <torvalds at linux-foundation.org>
Date: Sun Sep 29 17:59:23 2019 -0700

    Revert "Revert "ext4: make __ext4_get_inode_loc plug""

I've benchmarked the Eoan kernel with these two patches and found theo
following speed improvements on an i7-3770 CPU @ 3.40GHz with 8GB and a
WDC WD10EZEX-21WN4A HDD (7200RPM, 64MB cache).

git grep of the kernel: 0.14%
building fwts: 0.40%
build stress-ng 0.45%
tar up kernel source: 7.6%
boot time of eoan cloud image: 10.5% 

So I think the speed improvements justifies the SRU.

== Regression potential ==

Minor change to ext4, which has been regression tested, so risk here is
small. The entropy change will alter the random number generation, but
I believe this does not change the cryptographical security of the random
numbers being generated, so think this change is not security risk.

Originally the ext4 change caused boot time user space regressions
because of the entropy change of this fix, but the random fix addresses
this, so I believe this risk is now zero.

Linus Torvalds (2):
  random: try to actively add entropy rather than passively wait for it
  Revert "Revert "ext4: make __ext4_get_inode_loc plug""

 drivers/char/random.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 fs/ext4/inode.c       |  3 +++
 2 files changed, 64 insertions(+), 1 deletion(-)

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2.7.4