From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <owner-linux-mm@kvack.org>
Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198])
	by kanga.kvack.org (Postfix) with ESMTP id DFB546B038C
	for <linux-mm@kvack.org>; Tue, 14 Mar 2017 14:07:51 -0400 (EDT)
Received: by mail-pf0-f198.google.com with SMTP id e129so311613708pfh.1
        for <linux-mm@kvack.org>; Tue, 14 Mar 2017 11:07:51 -0700 (PDT)
Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81])
        by mx.google.com with ESMTPS id v5si15386714pgv.254.2017.03.14.11.07.50
        for <linux-mm@kvack.org>
        (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
        Tue, 14 Mar 2017 11:07:50 -0700 (PDT)
Date: Tue, 14 Mar 2017 11:07:38 -0700
From: "Darrick J. Wong" <darrick.wong@oracle.com>
Subject: Re: [PATCH v2] xfs: remove kmem_zalloc_greedy
Message-ID: <20170314180738.GV5280@birch.djwong.org>
References: <20170308003528.GK5280@birch.djwong.org>
 <20170314165745.GB28800@wotan.suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170314165745.GB28800@wotan.suse.de>
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Brian Foster <bfoster@redhat.com>, Michal Hocko <mhocko@kernel.org>, Christoph Hellwig <hch@lst.de>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, Xiong Zhou <xzhou@redhat.com>, linux-xfs@vger.kernel.org, linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>, linux-fsdevel@vger.kernel.org, Michal Hocko <mhocko@suse.com>, Dave Chinner <david@fromorbit.com>, sebastian.parschauer@suse.com, AlNovak@suse.com, jack@suse.cz

On Tue, Mar 14, 2017 at 05:57:45PM +0100, Luis R. Rodriguez wrote:
> On Tue, Mar 07, 2017 at 04:35:28PM -0800, Darrick J. Wong wrote:
> > The sole remaining caller of kmem_zalloc_greedy is bulkstat, which uses
> > it to grab 1-4 pages for staging of inobt records.  The infinite loop in
> > the greedy allocation function is causing hangs[1] in generic/269, so
> > just get rid of the greedy allocator in favor of kmem_zalloc_large.
> > This makes bulkstat somewhat more likely to ENOMEM if there's really no
> > pages to spare, but eliminates a source of hangs.
> > 
> > [1] http://lkml.kernel.org/r/20170301044634.rgidgdqqiiwsmfpj%40XZHOUW.usersys.redhat.com
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > v2: remove single-page fallback
> > ---
> 
> Since this fixes a hang how about *at the very least* a respective Fixes tag ?
> This fixes an existing hang so what are the stable considerations here ? I
> realize the answer is not easy but figured its worth asking.

I didn't think it was appropriate to "Fixes: 77e4635ae1917" since we're
not fixing _greedy so much as we are killing it.  The patch fixes an
infinite retry hang when bulkstat tries a memory allocation that cannot
be satisfied; and having done that, realizes there are no remaining
callers of _greedy and garbage collects it.  The code that was there
before also seems capable of sleeping forever, I think.

So the minimally invasive fix is to apply the allocation conversion in
bulkstat, and if there aren't any other callers of _greedy then you can
get rid of it too.

> FWIW I trace kmem_zalloc_greedy()'s introduction back to 2006 77e4635ae1917
> ("[XFS] Add a greedy allocation interface, allocating within a min/max size
> range.") through v2.6.19 days...

--D

> 
>   Luis
> --
> To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>