Re: [PATCH] ext4: remove unnecessary operation in ext4_mb_normalize_group_request()

["Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>]

On Fri, 26 Mar 2010 21:44:33 +0800, jing zhang <zj.barak@gmail.com> wrote:
> 2010/3/26, Aneesh Kumar K. V <aneesh.kumar@linux.vnet.ibm.com>:
> > On Thu, 25 Mar 2010 22:54:21 +0800, jing zhang <zj.barak@gmail.com> wrote:
> >> From: Jing Zhang <zj.barak@gmail.com>
> >>
> >> Date: Wed Mar 25  22:55:04   2010
> >>
> >> Checking bug seems not at right place, and the function itself should
> >> be inlined.
> >>
> >> Cc: Theodore Ts'o <tytso@mit.edu>
> >> Cc: Andreas Dilger <adilger@sun.com>
> >> Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
> >> Cc: "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>
> >> Signed-off-by: Jing Zhang <zj.barak@gmail.com>
> >>
> >> ---
> >>
> >> --- linux-2.6.32/fs/ext4/mballoc.c	2009-12-03 11:51:22.000000000 +0800
> >> +++ ext4_mm_leak/mballoc-10.c	2010-03-25 22:44:00.000000000 +0800
> >> @@ -2786,9 +2786,7 @@ out_err:
> >>  static void ext4_mb_normalize_group_request(struct
> >> ext4_allocation_context *ac)
> >>  {
> >>  	struct super_block *sb = ac->ac_sb;
> >> -	struct ext4_locality_group *lg = ac->ac_lg;
> >>
> >> -	BUG_ON(lg == NULL);
> >>  	if (EXT4_SB(sb)->s_stripe)
> >>  		ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_stripe;
> >>  	else
> >
> > That BUG_ON is to ensure that the allocation context is actually having
> > a locality group which is needed for group allocation request.
> >
> > -aneesh
> >
> 
> Please check
> 1, the 3 lines at the end of ext4_mb_group_or_file()
> 2, the function name of this patch
> 

What i wanted to mention was the BUG_ON is there to ensure that we don't
call ext4_mb_normalize_group_request on non group enabled allocation
context by programming mistake. Doing that would cause ac_g_ex.fe_len
to change. So that BUG_ON is there to capture a programming error. 

-aneesh