|From:||Al Viro <viro-AT-ZenIV.linux.org.uk>|
|To:||Christoph Lameter <clameter-AT-sgi.com>|
|Subject:||Re: Major regression on hackbench with SLUB (more numbers)|
|Date:||Wed, 26 Dec 2007 22:16:32 +0000|
|Cc:||Theodore Tso <tytso-AT-mit.edu>, Andi Kleen <andi-AT-firstfloor.org>, Willy Tarreau <w-AT-1wt.eu>, Steven Rostedt <rostedt-AT-goodmis.org>, Linus Torvalds <torvalds-AT-linux-foundation.org>, Ingo Molnar <mingo-AT-elte.hu>, Peter Zijlstra <a.p.zijlstra-AT-chello.nl>, LKML <linux-kernel-AT-vger.kernel.org>, Andrew Morton <akpm-AT-linux-foundation.org>, Christoph Hellwig <hch-AT-infradead.org>, "Rafael J. Wysocki" <rjw-AT-sisk.pl>|
On Wed, Dec 26, 2007 at 01:31:35PM -0800, Christoph Lameter wrote: > On Mon, 24 Dec 2007, Theodore Tso wrote: > > > So two questions: why isn't -f the default? And is /sys/slab > > Because it gives misleading output. It displays the name of the first > of multiple slabs that share the same storage structures. Erm... Let me spell it out: current lifetime rules are completely broken. As it is, create/destroy/create cache sequence will do kobject_put() on kfree'd object. Even without people playing with holding sysfs files open or doing IO on those. a) you have kobject embedded into struct with the lifetime rules of its own. When its refcount hits zero you kfree() the sucker, even if you still have references to embedded kobject. b) your symlinks stick around. Even when cache is long gone you still have a sysfs symlink with its embedded kobject as a target. They are eventually removed when cache with the same name gets created. _Then_ you get the target kobject dropped - when the memory it used to be in had been freed for hell knows how long and reused by something that would not appreciate slub.c code suddenly deciding to decrement some word in that memory. c) you leak references to these kobject; kobject_del() only removes it from the tree undoing the effect of kobject_add() and you still need kobject_put() to deal with the last reference. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to firstname.lastname@example.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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