From: Dave Hansen <haveblue@us.ibm.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: akpm@osdl.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 24/25] r/o bind mounts: track number of mount writers
Date: Mon, 24 Sep 2007 12:28:11 -0700 [thread overview]
Message-ID: <1190662091.26982.246.camel@localhost> (raw)
In-Reply-To: <20070924175411.GA2314@infradead.org>
On Mon, 2007-09-24 at 18:54 +0100, Christoph Hellwig wrote:
> As we already say in various messages the percpu counters in here
> look rather fishy. I'd recomment to take a look at the per-cpu
> superblock counters in XFS as they've been debugged quite well
> now and could probably be lifted into a generic library for this
> kind of think. The code is mostly in fs/xfs/xfs_mount.c can
> can be spotted by beeing under #ifdef HAVE_PERCPU_SB.
>
> It also handles cases like hotplug cpu nicely that this code
> seems to work around by always iterating over all possible cpus
> which might not be nice on a dual core laptop with a distro kernel
> that also has to support big iron.
I'll take a look at xfs to see what I can get out of it.
There are basically two times when you have to do this
for_each_possible_cpu() stuff:
1. when doing a r/w->r/o transition, which is rare, and
certainly not a fast path
2. Where the per-cpu writer count underflows. This requires
a _minimum_ of 1<<16 file opens (configurable) each of which
is closed on a different cpu than it was opened on. Even
if you were trying, I'm not sure you'd notice the overhead.
-- Dave
next prev parent reply other threads:[~2007-09-24 19:28 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-20 19:52 [PATCH 00/25] Read-only bind mounts Dave Hansen
2007-09-20 19:52 ` [PATCH 01/25] filesystem helpers for custom 'struct file's Dave Hansen
2007-09-20 19:52 ` [PATCH 02/25] rearrange may_open() to be r/o friendly Dave Hansen
2007-09-20 19:52 ` [PATCH 03/25] give may_open() a local 'mnt' variable Dave Hansen
2007-09-20 19:57 ` Christoph Hellwig
2007-09-20 19:52 ` [PATCH 04/25] create cleanup helper svc_msnfs() Dave Hansen
2007-09-20 19:52 ` [PATCH 05/25] r/o bind mounts: stub functions Dave Hansen
2007-09-20 19:52 ` [PATCH 06/25] elevate write count open()'d files Dave Hansen
2007-11-28 8:41 ` Andrew Morton
2007-11-28 17:33 ` Dave Hansen
2007-09-20 19:52 ` [PATCH 07/25] r/o bind mounts: elevate write count for some ioctls Dave Hansen
2007-09-21 8:17 ` Andrew Morton
2007-09-21 21:15 ` Dave Hansen
2007-09-26 1:34 ` [RFC] detect missed mnt_want_write() calls Dave Hansen
2007-09-21 23:03 ` [PATCH 07/25] r/o bind mounts: elevate write count for some ioctls Andrew Morton
2007-09-21 23:39 ` Dave Hansen
2007-09-21 23:47 ` Andrew Morton
2007-09-20 19:52 ` [PATCH 08/25] elevate writer count for chown and friends Dave Hansen
2007-09-20 19:53 ` [PATCH 09/25] make access() use mnt check Dave Hansen
2007-09-20 19:53 ` [PATCH 10/25] elevate mnt writers for callers of vfs_mkdir() Dave Hansen
2007-09-20 19:53 ` [PATCH 11/25] elevate write count during entire ncp_ioctl() Dave Hansen
2007-09-20 19:53 ` [PATCH 12/25] elevate write count for link and symlink calls Dave Hansen
2007-09-20 19:53 ` [PATCH 13/25] elevate mount count for extended attributes Dave Hansen
2007-09-20 19:53 ` [PATCH 14/25] elevate write count for file_update_time() Dave Hansen
2007-09-20 19:53 ` [PATCH 15/25] unix_find_other() elevate write count for touch_atime() Dave Hansen
2007-09-20 19:53 ` [PATCH 16/25] elevate write count over calls to vfs_rename() Dave Hansen
2007-09-20 19:53 ` [PATCH 17/25] nfs: check mnt instead of superblock directly Dave Hansen
2007-09-20 19:53 ` [PATCH 18/25] elevate writer count for do_sys_truncate() Dave Hansen
2007-09-20 19:53 ` [PATCH 19/25] elevate write count for do_utimes() Dave Hansen
2007-09-20 19:53 ` [PATCH 20/25] elevate write count for do_sys_utime() and touch_atime() Dave Hansen
2007-09-20 19:53 ` [PATCH 21/25] sys_mknodat(): elevate write count for vfs_mknod/create() Dave Hansen
2007-09-20 19:53 ` [PATCH 22/25] elevate mnt writers for vfs_unlink() callers Dave Hansen
2007-09-20 19:53 ` [PATCH 23/25] do_rmdir(): elevate write count Dave Hansen
2007-09-20 19:53 ` [PATCH 24/25] r/o bind mounts: track number of mount writers Dave Hansen
2007-09-24 6:17 ` Andrew Morton
2007-09-24 14:34 ` Arjan van de Ven
2007-09-24 22:06 ` Dave Hansen
2007-09-24 22:25 ` Andrew Morton
2007-09-24 23:05 ` Dave Hansen
2007-09-24 23:15 ` Andrew Morton
2007-09-25 16:10 ` Dave Hansen
2007-09-24 17:54 ` Christoph Hellwig
2007-09-24 19:10 ` Andrew Morton
2007-09-24 19:24 ` Christoph Hellwig
2007-09-24 19:28 ` Dave Hansen [this message]
2007-09-24 19:42 ` Andrew Morton
2007-10-01 18:06 ` Dave Hansen
2007-09-20 19:53 ` [PATCH 25/25] honor r/w changes at do_remount() time Dave Hansen
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