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    SubjectRe: [PATCH 0/7] breaking the global file_list_lock
    On Sun, Jan 28, 2007 at 02:43:25PM +0000, Christoph Hellwig wrote:
    > On Sun, Jan 28, 2007 at 12:51:18PM +0100, Peter Zijlstra wrote:
    > > This patch-set breaks up the global file_list_lock which was found to be a
    > > severe contention point under basically any filesystem intensive workload.
    > Benchmarks, please. Where exactly do you see contention for this?
    > filesystem intensive workload apparently means namespace operation heavy
    > workload, right? The biggest bottleneck I've seen with those is dcache lock.
    > Even if this is becoming a real problem there must be simpler ways to fix
    > this than introducing various new locking primitives and all kinds of
    > complexity.

    One good way to fix scalability without all this braindamage is
    to get rid of sb->s_files. Current uses are:

    - fs/dquot.c:add_dquot_ref()

    This performs it's actual operation on inodes. We should
    be able to check inode->i_writecount to see which inodes
    need quota initialization.

    - fs/file_table.c:fs_may_remount_ro()

    This one is gone in Dave Hansens per-mountpoint r/o patchkit

    - fs/proc/generic.c:proc_kill_inodes()

    This can be done with a list inside procfs.

    - fs/super.c:mark_files_ro()

    This one is only used for do_emergency_remount(), which is
    and utter hack. It might be much better to just deny any
    kind of write access through a superblock flag here.

    - fs/selinuxfs.c:sel_remove_bools()

    Utter madness. I have no idea how this ever got merged.
    Maybe the selinux folks can explain what crack they were
    on when writing this. The problem would go away with
    a generic rewoke infrastructure.

    Once sb->s_files is gone we can also kill of fu_list entirely and
    replace it by a list head entirely in the tty code and make the lock
    for it per-tty.
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      Last update: 2007-01-28 16:15    [W:0.040 / U:22.776 seconds]
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