linux-kernel - Re: [RFC PATCH v1 1/3] mm: teach mm by current context info to not do I/O during memory allocation

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Date:	Wed, 17 Oct 2012 09:54:09 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, linux-pm@...r.kernel.org,
	Jiri Kosina <jiri.kosina@...e.com>, Mel Gorman <mel@....ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-mm <linux-mm@...ck.org>
Subject: Re: [RFC PATCH v1 1/3] mm: teach mm by current context info to not do
 I/O during memory allocation

On Wed, Oct 17, 2012 at 4:19 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> The patch seems reasonable to me.  I'd like to see some examples of
> these resume-time callsite which are performing the GFP_KERNEL
> allocations, please.  You have found some kernel bugs, so those should
> be fully described.

There are two examples on 2/3 and 3/3 of the patchset, see below link:

        http://marc.info/?l=linux-kernel&m=135040325717213&w=2
        http://marc.info/?l=linux-kernel&m=135040327317222&w=2

Sorry for not Cc them to linux-mm because I am afraid of making noise
in mm list.

>
> This is just awful.  Why oh why do we write code in macros when we have
> a nice C compiler?

The two helpers are following style of local_irq_save() and
local_irq_restore(), so that people can use them easily, that is
why I define them as macro instead of inline.

>
> These can all be done as nice, clean, type-safe, documented C
> functions.  And if they can be done that way, they *should* be done
> that way!
>
> And I suggest that a better name for memalloc_noio_save() is
> memalloc_noio_set().  So this:

IMO, renaming as memalloc_noio_set() might not be better than _save
because the _set name doesn't indicate that the flag should be stored first.

>
> static inline unsigned memalloc_noio(void)
> {
>         return current->flags & PF_MEMALLOC_NOIO;
> }
>
> static inline unsigned memalloc_noio_set(unsigned flags)
> {
>         unsigned ret = memalloc_noio();
>
>         current->flags |= PF_MEMALLOC_NOIO;
>         return ret;
> }
>
> static inline unsigned memalloc_noio_restore(unsigned flags)
> {
>         current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags;
> }
>
> (I think that's correct?  It's probably more efficient this way).

Yes, it is correct and more clean, and I will take it.

Thanks,
--
Ming Lei
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