linux-kernel - ext4 extent status tree LRU locking

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <51B7B128.60909@intel.com>
Date:	Tue, 11 Jun 2013 16:22:16 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	linux-ext4@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	"Theodore Ts'o" <tytso@....edu>, Jan kara <jack@...e.cz>
Subject: ext4 extent status tree LRU locking

I've got a test case which I intended to use to stress the VM a bit.  It
fills memory up with page cache a couple of times.  It essentially runs
30 or so cp's in parallel.

98% of my CPU is system time, and 96% of _that_ is being spent on the
spinlock in ext4_es_lru_add().  I think the LRU list head and its lock
end up being *REALLY* hot cachelines and are *the* bottleneck on this
test.  Note that this is _before_ we go in to reclaim and actually start
calling in to the shrinker.  There is zero memory pressure in this test.

I'm not sure the benefits of having a proper in-order LRU during reclaim
outweigh such a drastic downside for the common case.

Any thoughts?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/