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SubjectRe: Strange performance change 59 -> 61/62
>>> I'm comparing 59-mjb6 to 61-mjb1 and notice some strange performance
>>> differences that I can't explain ... not a big drop, but odd.
>>> ...
>>>
>>> 1562 .text.lock.file_table
>>> 583 dentry_open
>>> 551 get_empty_filp
>>
>> The first one here is fget(). That's causing problems on ppc64 as well - the
>> machine is spending as long in fget as it is in copy_foo_user() in dbench
>> runs.
>>
>> One possibility is that we're calling fget() more often than previously,
>> although that would be rather odd. Can you add the below patch, and monitor
>> /proc/meminfo:nr_fgets?

Some more stats ... which look rather suspicious. 600% increase for
dentry_open and __mark_inode_dirty? Hmmmmm.

5198 35.9% .text.lock.file_table
4562 2.6% total
736 19.5% get_empty_filp
568 617.4% dentry_open
510 607.1% __mark_inode_dirty
285 11.3% atomic_dec_and_lock
272 11.9% __fput
230 23.0% dput
167 8.9% file_move
159 1.0% page_remove_rmap
128 67.7% vma_merge
118 17.1% current_kernel_time
66 1.0% page_add_rmap
62 0.0% can_vma_merge_after
50 2.3% do_schedule
...
-56 -16.0% do_brk
-67 -8.5% sys_brk
-73 -0.5% do_anonymous_page
-83 -45.6% do_lookup
-109 -11.3% fd_install
-114 -3.9% __copy_from_user_ll
-133 -10.9% do_generic_mapping_read
-282 -18.4% vfs_read
-314 -34.4% file_ra_state_init
-373 -7.7% vm_enough_memory
-445 -5.5% d_lookup
-1693 -3.8% default_idle

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