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

On Wed, 17 Oct 2012 09:54:09 +0800
Ming Lei <ming.lei@canonical.com> wrote:

> On Wed, Oct 17, 2012 at 4:19 AM, Andrew Morton
> <akpm@linux-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&...
>         http://marc.info/?l=linux-kernel&m=135040327317222&...
> 
> Sorry for not Cc them to linux-mm because I am afraid of making noise
> in mm list.

Don't worry about mailing list noise ;)

> >
> > 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.

local_irq_save() and local_irq_restore() were mistakes :( It's silly to
write what appears to be a C function and then have it operate like
Pascal (warning: I last wrote some Pascal in 66 B.C.).

> >
> > 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.

You could add __must_check to the function definition to ensure that
all callers save its return value.

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