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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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