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Re: [linux-lvm] Question about VFS Locking patch, why is a changeneeded?



Chris,

Thanks for the info !

-steve

Chris Mason wrote:

On Thu, 2003-04-17 at 20:43, Steven Dake wrote:


Folks,

I was analyzing the VFS locking patch and I wanted to know if someone could explain the purpose of a change in the reiserfs for me:

The change is:
Index: linus.21/fs/reiserfs/super.c
--- linus.21/fs/reiserfs/super.c Fri, 11 Jan 2002 10:14:59 -0500 root (linux/41_super.c 1.2.2.1.2.1.1.1 644)
+++ linus.21(w)/fs/reiserfs/super.c Mon, 28 Jan 2002 13:50:56 -0500 root (linux/41_super.c 1.2.2.1.2.1.1.1 644)
@@ -66,7 +66,7 @@
reiserfs_prepare_for_journal(s, SB_BUFFER_WITH_SB(s), 1);
journal_mark_dirty(&th, s, SB_BUFFER_WITH_SB (s));
reiserfs_block_writes(&th) ;
- journal_end(&th, s, 1) ;
+ journal_end_sync(&th, s, 1) ;
}
s->s_dirt = dirty;
unlock_kernel() ;


I tried LVM with and without this change even under heavy load and LVM can still create mountable snapshots of a reiser filesystem without the change. Why is it there?



journal_end will do an asynchronous commit, which means it won't wait for the journal to actually finish writing to disk. journal_end_sync will wait until the commit is fully on disk.

In most cases, the reiserfs_block_writes call is sufficient and the
journal_end_sync change isn't needed, but there are a few corner cases
depending on the number of log writers where journal_end_sync is
required.

-chris



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