[linux-lvm] Question about VFS Locking patch, why is a change needed?

[linux-lvm] Question about VFS Locking patch, why is a change needed?

[Steven Dake]

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?

Thanks
-steve

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

[Chris Mason]

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

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

[Steven Dake]

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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>
>
>
>  
>