linux-kernel - Re: [13/17] Virtual compound page freeing in interrupt context

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Message-Id: <200709190636.59631.nickpiggin@yahoo.com.au>
Date:	Wed, 19 Sep 2007 06:36:59 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
Cc:	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [13/17] Virtual compound page freeing in interrupt context

On Wednesday 19 September 2007 13:36, Christoph Lameter wrote:
> If we are in an interrupt context then simply defer the free via a
> workqueue.
>
> In an interrupt context it is not possible to use vmalloc_addr() to
> determine the vmalloc address. So add a variant that does that too.
>
> Removing a virtual mappping *must* be done with interrupts enabled
> since tlb_xx functions are called that rely on interrupts for
> processor to processor communications.

These things will clash drastically with my lazy TLB flushing and scalability
work. Actually the lazy TLB flushing will provide a natural way to defer
unmapping at interrupt time, and the scalability work should make it
easier to vmap from interrupt context too, if you really need that.

>
> Signed-off-by: Christoph Lameter <clameter@....com>
>
> ---
>  mm/page_alloc.c |   23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c	2007-09-18 20:10:55.000000000 -0700
> +++ linux-2.6/mm/page_alloc.c	2007-09-18 20:11:40.000000000 -0700
> @@ -1297,7 +1297,12 @@ abort:
>  	return NULL;
>  }
>
> -static void vcompound_free(void *addr)
> +/*
> + * Virtual Compound freeing functions. This is complicated by the vmalloc
> + * layer not being able to free virtual allocations when interrupts are
> + * disabled. So we defer the frees via a workqueue if necessary.
> + */
> +static void __vcompound_free(void *addr)
>  {
>  	struct page **pages = vunmap(addr);
>  	int i;
> @@ -1320,6 +1325,22 @@ static void vcompound_free(void *addr)
>  	kfree(pages);
>  }
>
> +static void vcompound_free_work(struct work_struct *w)
> +{
> +	__vcompound_free((void *)w);
> +}
> +
> +static void vcompound_free(void *addr)
> +{
> +	if (in_interrupt()) {
> +		struct work_struct *w = addr;
> +
> +		INIT_WORK(w, vcompound_free_work);
> +		schedule_work(w);
> +	} else
> +		__vcompound_free(addr);
> +}
> +
>  /*
>   * This is the 'heart' of the zoned buddy allocator.
>   */
-
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