netdev - Re: [PATCH 03/29] mm: allow PF_MEMALLOC from softirq context

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Date:	Thu, 22 Feb 2007 10:48:08 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	netdev@...r.kernel.org,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Thomas Graf <tgraf@...g.ch>, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 03/29] mm: allow PF_MEMALLOC from softirq context

On Thu, 2007-02-22 at 10:16 +0100, Peter Zijlstra wrote:
> On Wed, 2007-02-21 at 16:53 +0100, Arjan van de Ven wrote:
> > > Index: linux-2.6-git/kernel/softirq.c
> > > ===================================================================
> > > --- linux-2.6-git.orig/kernel/softirq.c	2006-12-14 10:02:18.000000000 +0100
> > > +++ linux-2.6-git/kernel/softirq.c	2006-12-14 10:02:52.000000000 +0100
> > > @@ -209,6 +209,8 @@ asmlinkage void __do_softirq(void)
> > >  	__u32 pending;
> > >  	int max_restart = MAX_SOFTIRQ_RESTART;
> > >  	int cpu;
> > > +	unsigned long pflags = current->flags;
> > > +	current->flags &= ~PF_MEMALLOC;
> > >  
> > >  	pending = local_softirq_pending();
> > >  	account_system_vtime(current);
> > > @@ -247,6 +249,7 @@ restart:
> > >  
> > >  	account_system_vtime(current);
> > >  	_local_bh_enable();
> > > +	current->flags = pflags;
> > 
> > this wipes out all the flags in one go.... evil.
> > What if something just selected this process for OOM killing? you nuke
> > that flag here again. Would be nicer if only the PF_MEMALLOC bit got
> > inherited in the restore path..
> 
> would something like this:
> 
> #define PF_PUSH(tsk, pflags, mask)		\
> do {						\
> 	(pflags) = ((tsk)->flags) & (mask);	\
> } while (0)
> 
> 
> #define PF_POP(tsk, pflags, mask)		\
> do {						\
> 	((tsk)->flags &= ~(mask);		\
> 	((tsk)->flags |= (pflags);		\
> } while (0)
> 
> be useful, or shall I just open code it in various places?

technically all you need is __get_bit and __set_bit() right?
(well a set_bit which sets to a value, not to always-1)

more generic name at least ;)

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

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