linux-kernel - Re: [PATCH 2/2] fs/aio.c: use get_user_pages_non_movable() to pin ring pages when support memory hotremove

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Date:	Mon, 4 Feb 2013 15:02:09 -0800
From:	Zach Brown <zab@...hat.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Lin Feng <linfeng@...fujitsu.com>, akpm@...ux-foundation.org,
	mgorman@...e.de, bcrl@...ck.org, viro@...iv.linux.org.uk,
	khlebnikov@...nvz.org, walken@...gle.com,
	kamezawa.hiroyu@...fujitsu.com, minchan@...nel.org,
	riel@...hat.com, rientjes@...gle.com,
	isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com,
	laijs@...fujitsu.com, jiang.liu@...wei.com, linux-mm@...ck.org,
	linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fs/aio.c: use get_user_pages_non_movable() to pin
 ring pages when support memory hotremove

> > index 71f613c..0e9b30a 100644
> > --- a/fs/aio.c
> > +++ b/fs/aio.c
> > @@ -138,9 +138,15 @@ static int aio_setup_ring(struct kioctx *ctx)
> >  	}
> >  
> >  	dprintk("mmap address: 0x%08lx\n", info->mmap_base);
> > +#ifdef CONFIG_MEMORY_HOTREMOVE
> > +	info->nr_pages = get_user_pages_non_movable(current, ctx->mm,
> > +					info->mmap_base, nr_pages,
> > +					1, 0, info->ring_pages, NULL);
> > +#else
> >  	info->nr_pages = get_user_pages(current, ctx->mm,
> >  					info->mmap_base, nr_pages, 
> >  					1, 0, info->ring_pages, NULL);
> > +#endif
> 
> Can't you hide this in your 1/1 patch, by providing this function as
> just a static inline wrapper around get_user_pages when
> CONFIG_MEMORY_HOTREMOVE is not enabled?

Yes, please.  Having callers duplicate the call site for a single
optional boolean input is unacceptable.

But do we want another input argument as a name?  Should aio have been
using get_user_pages_fast()? (and so now _fast_non_movable?)

I wonder if it's time to offer the booleans as a _flags() variant, much
like the current internal flags for __get_user_pages().  The write and
force arguments are already booleans, we have a different fast api, and
now we're adding non-movable.  The NON_MOVABLE flag would be 0 without
MEMORY_HOTREMOVE, easy peasy.

Turning current callers' mysterious '1, 1' in to 'WRITE|FORCE' might
also be nice :).

No?

- z
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