Messages in this thread | | | Date | Mon, 04 Dec 2006 10:51:19 -0600 | From | Russell Cattelan <> | Subject | Re: [PATCH] prune_icache_sb |
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Wendy Cheng wrote:
> Andrew Morton wrote: > >> On Thu, 30 Nov 2006 11:05:32 -0500 >> Wendy Cheng <wcheng@redhat.com> wrote: >> >> >> >>> >>> The idea is, instead of unconditionally dropping every buffer >>> associated with the particular mount point (that defeats the purpose >>> of page caching), base kernel exports the "drop_pagecache_sb()" call >>> that allows page cache to be trimmed. More importantly, it is >>> changed to offer the choice of not randomly purging any buffer but >>> the ones that seem to be unused (i_state is NULL and i_count is >>> zero). This will encourage filesystem(s) to pro actively response to >>> vm memory shortage if they choose so. >>> >> >> >> argh. >> >> > I read this as "It is ok to give system admin(s) commands (that this > "drop_pagecache_sb() call" is all about) to drop page cache. It is, > however, not ok to give filesystem developer(s) this very same > function to trim their own page cache if the filesystems choose to do > so" ? > >> In Linux a filesystem is a dumb layer which sits between the VFS and the >> I/O layer and provides dumb services such as reading/writing inodes, >> reading/writing directory entries, mapping pagecache offsets to disk >> blocks, etc. (This model is to varying degrees incorrect for every >> post-ext2 filesystem, but that's the way it is). >> >> > 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
Does this change help fix gfs lock ordering problem as well?
-Russell Cattelan cattelan@xfs.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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