Messages in this thread | | | Date | Wed, 25 Mar 2009 10:47:05 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 2/5] mm: remove unlikly NULL from kfree |
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On Wed, 25 Mar 2009, Pekka Enberg wrote:
> On Wed, 2009-03-25 at 01:02 -0700, Hua Zhong wrote: > >> > But those are _error handling paths_ (at least supposed to be). I > >> > wonder which call-sites are responsible for this. Can frtrace help us > >> > here? > >> > >> I am not sure why you call these error paths. > >> > >> I submitted the same patch two years ago, and you are still holding the same > >> argument. > >> > >> http://www.archivum.info/linux.kernel/2006-04/msg06042.html > >> > >> Have you used likely profiler? These are real numbers. If you insist on > >> calling them error paths then error paths are obviously the norm. > > On Wed, Mar 25, 2009 at 10:06 AM, Pekka Enberg <penberg@cs.helsinki.fi> wrote: > > I am not denying the results, I am just saying that they don't make much > > sense to me. Like I said, I would love to see the actual call-sites to > > prove my argument wrong. > > OK, so according to Steven, audit_syscall_exit() is one such call-site > that shows up in the traces. I don't really understand what's going on > there but if it is sane, maybe that warrants the removal of unlikely() > from kfree(). Hmm?
After disabling AUDIT_SYSCALLS I have this:
# cat /debug/tracing/trace | sort -u
record_nulls: ptr=(null) (ext3_get_acl+0x1e0/0x3f0 [ext3]) record_nulls: ptr=(null) (free_bitmap+0x29/0x70) record_nulls: ptr=(null) (free_tty_struct+0x1d/0x40) record_nulls: ptr=(null) (ftrace_graph_exit_task+0x1e/0x20) record_nulls: ptr=(null) (inet_sock_destruct+0x1cb/0x2a0) record_nulls: ptr=(null) (ip_cork_release+0x24/0x50) record_nulls: ptr=(null) (keyctl_join_session_keyring+0x5a/0x70) record_nulls: ptr=(null) (key_user_lookup+0x183/0x220) record_nulls: ptr=(null) (kobject_set_name_vargs+0x43/0x50) record_nulls: ptr=(null) (netlink_release+0x1a4/0x2f0) record_nulls: ptr=(null) (release_sysfs_dirent+0x20/0xc0) record_nulls: ptr=(null) (sysfs_open_file+0x1c8/0x3e0) record_nulls: ptr=(null) (tty_write+0x16a/0x290)
I added a hook to only record when NULL is passed into kfree.
Also note, that after disabling AUDIT_SYSCALLS I now only have roughly 7% NULL hit rate. Still, unlikely is probably not a benefit here.
correct incorrect % Function File Line ------- --------- - -------- ---- ---- 108129 8214 7 kfree slub.c 2796
And yes, this is a different kernel than the patch. This is running on tip and not 2.6.29, and also, you can see, uses slub.c not slab.c. The reason I changed was because:
1) it has better tracing utilities 2) included your trace point patch ;-)
The header is still messed up, because I'm using the kmemtrace branch and not the ftrace branch, but I had better go back and make sure they are fixed.
-- Steve
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