linux-ext4 - Re: [PATCH] ext4: group cache is added in ext4_mb_discard

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Message-ID: <20100407144603.GO23670@thunk.org>
Date:	Wed, 7 Apr 2010 10:46:03 -0400
From:	tytso@....edu
To:	jing zhang <zj.barak@...il.com>
Cc:	Andreas Dilger <adilger@....com>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH] ext4: group cache is added in
 ext4_mb_discard_preallocations()

On Wed, Apr 07, 2010 at 08:58:36PM +0800, jing zhang wrote:
> 2010/4/7, tytso@....edu <tytso@....edu>:
> > On Thu, Apr 01, 2010 at 08:34:41PM +0800, jing zhang wrote:
> >>
> >> --- linux-2.6.32/fs/ext4/mballoc.c	2009-12-03 11:51:22.000000000 +0800
> >> +++ ext4_mm_leak/mballoc-14.c	2010-04-01 20:35:58.000000000 +0800
> >> @@ -4299,7 +4299,7 @@ repeat:
> >>  		}
> >>  	} else {
> >>  		freed  = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
> >> -		if (freed)
> >> +		if (freed && freed >= ac->ac_o_ex.fe_len)
> >>  			goto repeat;
> >>  		*errp = -ENOSPC;
> >>  		ac->ac_b_ex.fe_len = 0;
> >
> > This is just wrong.
> >
> > Since you didn't give a justification, I'm not sure why you think it
> > is correct.
> >
> 
> Though freed, is the amount freed bigger than needed?
> If not, it seems unnecessary to repeat.

You don't understand the code, I think.  If we've freed up any number
of blocks, it makes sense to use those blocks right away.  Mballoc()
is allowed to return fewer blocks than what was requested.

   	      	    	     	 - Ted
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