Date: Tue, 24 Nov 2009 19:46:25 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Adrian Hunter <adrian.hunter@nokia.com>
Subject: Re: [PATCH 4/7] nandsim: Don't use PF_MEMALLOC
Cc: kosaki.motohiro@jp.fujitsu.com,
       "Bityutskiy Artem (Nokia-D/Helsinki)" <Artem.Bityutskiy@nokia.com>,
       LKML <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       David Woodhouse <David.Woodhouse@intel.com>,
       "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>
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Hi

Thank you for this useful comments.

> > I vaguely remember Adrian (CCed) did this on purpose. This is for the
> > case when nandsim emulates NAND flash on top of a file. So there are 2
> > file-systems involved: one sits on top of nandsim (e.g. UBIFS) and the
> > other owns the file which nandsim uses (e.g., ext3).
> > 
> > And I really cannot remember off the top of my head why he needed
> > PF_MEMALLOC, but I think Adrian wanted to prevent the direct reclaim
> > path to re-enter, say UBIFS, and cause deadlock. But I'd thing that all
> > the allocations in vfs_read()/vfs_write() should be GFP_NOFS, so that
> > should not be a probelm?
> > 
> 
> Yes it needs PF_MEMALLOC to prevent deadlock because there can be a
> file system on top of nandsim which, in this case, is on top of another
> file system.
> 
> I do not see how mempools will help here.
> 
> Please offer an alternative solution.

I have few questions.

Can you please explain more detail? Another stackable filesystam
(e.g. ecryptfs) don't have such problem. Why nandsim have its issue?
What lock cause deadlock?


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