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From: Nick Piggin <npiggin@suse.de>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	Hugh Dickins <hugh@veritas.com>, Tejun Heo <tj@kernel.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@infradead.org>,
	"Eric W. Biederman" <ebiederm@aristanetworks.com>
Subject: Re: [PATCH 03/23] vfs: Generalize the file_list
Date: Tue, 2 Jun 2009 09:06:42 +0200
Message-ID: <20090602070642.GD31556@wotan.suse.de> (raw)
In-Reply-To: <1243893048-17031-3-git-send-email-ebiederm@xmission.com>

On Mon, Jun 01, 2009 at 02:50:28PM -0700, Eric W. Biederman wrote:
> From: Eric W. Biederman <ebiederm@xmission.com>
> 
> In the implementation of revoke it is desirable to find all of the
> files we want to operation on.  Currently tty's and mark_files_ro
> use the file_list for this, and this patch generalizes the file
> list so it can be used more efficiently.
> 
> This patch starts by introducing struct file_list making the file
> list a first class object.  file_list_lock and file_list_unlock
> are modified to take this object, making it clear which file_list
> we intended to lock.
> 
> file_move is transformed into file_list_add taking a file_list and not
> allowing the movement of one file to another. __dentry_open
> is modified to support this by only adding normal files in open,
> special files have always been ignored when walking the file_list.
> __dentry_open skipping special files allows __ptmx_open and __tty_open
> to safely call file_add as they are adding the file to the file_list
> for the first time.
> 
> file_kill has been renamed file_list_del to make it clear what it is
> doing and to keep from confusing it with a more revoke like operation.
> 
> put_filp has been modified to not take file_list_del as we are never
> on a file_list when put_filp is called.
> 
> fs_may_remount_ro and mark_files_ro have been modified to walk the
> inode list to find all of the inodes and then to walk the file list
> on those inodes.  It can be a slightly longer walk as we frequently
> cache inodes that we do not have open but the overall complexity
> should be about the same,

Well not really. I have a couple of orders of magnitude more cached
inodes than open files here.


> these are slow path functions, and it
> gives us much greater flexibility overall.

Define flexibility. Walking the sb's file list and checking for
equality with the inode in question gives the same functionality,
just different performance profile.


> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -699,6 +699,11 @@ static inline int mapping_writably_mapped(struct address_space *mapping)
>  	return mapping->i_mmap_writable != 0;
>  }
>  
> +struct file_list {
> +	spinlock_t		lock;
> +	struct list_head	list;
> +};
> +
>  /*
>   * Use sequence counter to get consistent i_size on 32-bit processors.
>   */
> @@ -764,6 +769,7 @@ struct inode {
>  	struct list_head	inotify_watches; /* watches on this inode */
>  	struct mutex		inotify_mutex;	/* protects the watches list */
>  #endif
> +	struct file_list	i_files;
>  
>  	unsigned long		i_state;
>  	unsigned long		dirtied_when;	/* jiffies of first dirtying */
> @@ -934,9 +940,15 @@ struct file {
>  	unsigned long f_mnt_write_state;
>  #endif
>  };
> -extern spinlock_t files_lock;
> -#define file_list_lock() spin_lock(&files_lock);
> -#define file_list_unlock() spin_unlock(&files_lock);
> +
> +static inline void file_list_lock(struct file_list *files)
> +{
> +	spin_lock(&files->lock);
> +}
> +static inline void file_list_unlock(struct file_list *files)
> +{
> +	spin_unlock(&files->lock);
> +}

I don't really like this. It's just a list head. Get rid of
all these wrappers and crap I'd say. In fact, starting with my
patch to unexport files_lock and remove these wrappers would
be reasonable, wouldn't it?

Increasing the size of the struct inode by 24 bytes hurts.
Even when you decrapify it and can reuse i_lock or something,
then it is still 16 bytes on 64-bit.

I haven't looked through all the patches... but this is to
speed up a slowpath operation, isn't it? Or does revoke
need to be especially performant?

So this patch is purely a perofrmance improvement? Then I think
it needs to be justified with numbers and the downsides (bloating
struct inode in particulra) to be changelogged.

  reply index

Thread overview: 99+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-04-11 12:01 [RFC][PATCH 0/9] File descriptor hot-unplug support Eric W. Biederman
2009-04-11 12:03 ` [RFC][PATCH 1/9] mm: Introduce remap_file_mappings Eric W. Biederman
2009-04-11 12:05 ` [RFC][PATCH 2/9] mm: Implement generic support for revoking a mapping Eric W. Biederman
2009-04-11 12:06 ` [RFC][PATCH 3/9] sysfs: Use remap_file_mappings Eric W. Biederman
2009-04-11 12:07 ` [RFC][PATCH 4/9] vfs: Generalize the file_list Eric W. Biederman
2009-04-11 12:08 ` [RFC][PATCH 5/9] vfs: Introduce basic infrastructure for revoking a file Eric W. Biederman
2009-04-14 22:12   ` Jonathan Corbet
2009-04-15  2:55     ` Eric W. Biederman
2009-04-11 12:10 ` [RFC][PATCH 6/9] vfs: Utilize fops_read_lock where appropriate Eric W. Biederman
2009-04-11 12:11 ` [RFC][PATCH 7/9] vfs: Optimize fops_read_lock Eric W. Biederman
2009-04-11 12:13 ` [RFC][PATCH 8/9] vfs: Implement generic revoked file operations Eric W. Biederman
2009-04-12 18:56   ` Jamie Lokier
2009-04-12 20:04     ` Eric W. Biederman
2009-04-12 20:31       ` Jamie Lokier
2009-04-12 21:53         ` Eric W. Biederman
2009-04-12 20:54       ` Eric W. Biederman
2009-04-12 21:02         ` Jamie Lokier
2009-04-12 23:06           ` Eric W. Biederman
2009-04-11 12:14 ` [RFC][PATCH 9/9] proc: Use the generic vfs revoke facility that now exists Eric W. Biederman
2009-04-11 15:58 ` [RFC][PATCH 0/9] File descriptor hot-unplug support Al Viro
2009-04-11 16:49   ` Eric W. Biederman
2009-04-11 16:56     ` Al Viro
2009-04-11 23:57       ` Eric W. Biederman
2009-04-12 20:21       ` Eric W. Biederman
2009-04-14  3:16 ` Tejun Heo
2009-04-14  7:39   ` Eric W. Biederman
2009-04-14  7:45     ` Tejun Heo
2009-04-14  8:27       ` Eric W. Biederman
2009-04-14  8:49         ` Tejun Heo
2009-04-14 15:07         ` Jamie Lokier
2009-04-14 19:09           ` Eric W. Biederman
2009-06-01 21:45 ` [PATCH 0/23] File descriptor hot-unplug support v2 Eric W. Biederman
2009-06-01 21:50   ` [PATCH 01/23] mm: Introduce revoke_file_mappings Eric W. Biederman
2009-06-01 22:25     ` Andrew Morton
2009-06-02  0:12       ` Eric W. Biederman
2009-06-01 21:50   ` [PATCH 02/23] vfs: Implement unpoll_file Eric W. Biederman
2009-06-06  8:08     ` Al Viro
2009-06-01 21:50   ` [PATCH 03/23] vfs: Generalize the file_list Eric W. Biederman
2009-06-02  7:06     ` Nick Piggin [this message]
2009-06-05 19:33       ` Eric W. Biederman
2009-06-09 10:38         ` Nick Piggin
2009-06-09 18:38           ` Eric W. Biederman
2009-06-10  6:05             ` Nick Piggin
2009-06-01 21:50   ` [PATCH 04/23] vfs: Introduce infrastructure for revoking a file Eric W. Biederman
2009-06-02  5:16     ` Pekka Enberg
2009-06-02  6:51       ` Eric W. Biederman
2009-06-02  7:08         ` Pekka Enberg
2009-06-02  7:14     ` Nick Piggin
2009-06-02 17:06       ` Linus Torvalds
2009-06-02 20:52         ` Eric W. Biederman
2009-06-03  6:37           ` Nick Piggin
2009-06-02 22:56       ` Eric W. Biederman
2009-06-03  6:38         ` Nick Piggin
2009-06-05  9:03     ` Miklos Szeredi
2009-06-05 19:06       ` Eric W. Biederman
2009-06-01 21:50   ` [PATCH 05/23] vfs: Teach lseek to use file_hotplug_lock Eric W. Biederman
2009-06-01 21:50   ` [PATCH 06/23] vfs: Teach read/write to use file_hotplug_read_lock Eric W. Biederman
2009-06-01 21:50   ` [PATCH 07/23] vfs: Teach sendfile,splice,tee,and vmsplice to use file_hotplug_lock Eric W. Biederman
2009-06-03 23:39     ` Badari Pulavarty
2009-06-05 19:37       ` Eric W. Biederman
2009-06-01 21:50   ` [PATCH 08/23] vfs: Teach readdir " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 09/23] vfs: Teach poll and select " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 10/23] vfs: Teach do_path_lookup " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 11/23] mm: Teach mmap " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 12/23] vfs: Teach fcntl " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 13/23] vfs: Teach ioctl " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 14/23] vfs: Teach flock " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 15/23] vfs: Teach fallocate, and filp_close " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 16/23] vfs: Teach fstatfs, fstatfs64, ftruncate, fchdir, fchmod, fchown " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 17/23] proc: Teach /proc/<pid>/fd " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 18/23] vfs: Teach epoll " Eric W. Biederman
2009-06-02 16:51     ` Davide Libenzi
2009-06-02 21:23       ` Eric W. Biederman
2009-06-02 21:52         ` Davide Libenzi
2009-06-02 22:51           ` Eric W. Biederman
2009-06-03 14:57             ` Davide Libenzi
2009-06-03 20:53               ` Eric W. Biederman
2009-06-04  0:50                 ` Davide Libenzi
2009-06-04  1:42                   ` Eric W. Biederman
2009-06-01 21:50   ` [PATCH 19/23] eventpoll: Fix comment Eric W. Biederman
2009-06-01 21:50   ` [PATCH 20/23] vfs: Teach aio to use file_hotplug_lock Eric W. Biederman
2009-06-01 21:50   ` [PATCH 21/23] vfs: Teach fsync " Eric W. Biederman
2009-06-01 21:50   ` [PATCH 22/23] vfs: Teach fadvice to file_hotplug_lock Eric W. Biederman
2009-06-01 21:50   ` [PATCH 23/23] vfs: Teach readahead to use the file_hotplug_lock Eric W. Biederman
2009-06-03 23:25     ` Badari Pulavarty
2009-06-06  8:03   ` [PATCH 0/23] File descriptor hot-unplug support v2 Al Viro
2009-06-08  9:41     ` Miklos Szeredi
2009-06-08 10:24       ` Jamie Lokier
2009-06-08 16:29       ` Al Viro
2009-06-08 16:44         ` Miklos Szeredi
2009-06-08 17:50           ` Al Viro
2009-06-08 18:01             ` Linus Torvalds
2009-06-08 18:50               ` Al Viro
2009-06-08 19:18                 ` Linus Torvalds
2009-06-09  6:42                   ` Eric W. Biederman
2009-06-09 10:52                     ` Nick Piggin
2009-06-09  5:50             ` Miklos Szeredi
2009-06-09  6:31               ` Eric W. Biederman
2009-06-09  6:22     ` Eric W. Biederman

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