linux-kernel - Re: [PATCH] prune_icache

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Date:	Mon, 04 Dec 2006 15:46:33 -0500
From:	Wendy Cheng <wcheng@...hat.com>
To:	Russell Cattelan <cattelan@...barn.com>
CC:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] prune_icache_sb

Russell Cattelan wrote:
> Wendy Cheng wrote:
>
>> Linux kernel, particularly the VFS layer, is starting to show signs 
>> of inadequacy as the software components built upon it keep growing. 
>> I have doubts that it can keep up and handle this complexity with a 
>> development policy like you just described (filesystem is a dumb 
>> layer ?). Aren't these DIO_xxx_LOCKING flags inside 
>> __blockdev_direct_IO() a perfect example why trying to do too many 
>> things inside vfs layer for so many filesystems is a bad idea ? By 
>> the way, since we're on this subject, could we discuss a little bit 
>> about vfs rename call (or I can start another new discussion thread) ?
>>
>> Note that linux do_rename() starts with the usual lookup logic, 
>> followed by "lock_rename", then a final round of dentry lookup, and 
>> finally comes to filesystem's i_op->rename call. Since lock_rename() 
>> only calls for vfs layer locks that are local to this particular 
>> machine, for a cluster filesystem, there exists a huge window between 
>> the final lookup and filesystem's i_op->rename calls such that the 
>> file could get deleted from another node before fs can do anything 
>> about it. Is it possible that we could get a new function pointer 
>> (lock_rename) in inode_operations structure so a cluster filesystem 
>> can do proper locking ?
>
> It looks like the ocfs2 guys have the similar problem?
>
> http://ftp.kernel.org/pub/linux/kernel/people/mfasheh/ocfs2/ocfs2_git_patches/ocfs2-upstream-linus-20060924/0009-PATCH-Allow-file-systems-to-manually-d_move-inside-of-rename.txt 
>
>
>

Thanks for the pointer. Same as ocfs2, under current VFS code, both 
GFS1/2 also need FS_ODD_RENAME flag for the rename problem - got an ugly 
~200 line draft patch ready for GFS1 (and am looking into GFS2 at this 
moment). The issue here is, for GFS, if vfs lock_rename() can call us, 
this complication can be greatly reduced. Will start another thread to 
see whether the wish can be granted.

-- Wendy

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