linux-kernel - Re: [patch] mm/slub: Move slab initialization into irq enabled region

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Message-ID: <20150710110242.25c84965@gandalf.local.home>
Date:	Fri, 10 Jul 2015 11:02:42 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch] mm/slub: Move slab initialization into irq enabled
 region

On Fri, 10 Jul 2015 12:07:13 -0000
Thomas Gleixner <tglx@...utronix.de> wrote:


>  /*
>   * Slab allocation and freeing
>   */
> @@ -1336,6 +1347,8 @@ static struct page *allocate_slab(struct
>  	struct page *page;
>  	struct kmem_cache_order_objects oo = s->oo;
>  	gfp_t alloc_gfp;
> +	void *start, *p;
> +	int idx, order;
>  
>  	flags &= gfp_allowed_mask;
>  
> @@ -1364,8 +1377,11 @@ static struct page *allocate_slab(struct
>  			stat(s, ORDER_FALLBACK);
>  	}
>  
> -	if (kmemcheck_enabled && page
> -		&& !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
> +	if (!page)
> +		goto out;

Since the above now looks like this:

	page = alloc_slab_page(s, alloc_gfp, node, oo);
	if (unlikely(!page)) {
		oo = s->min;
		alloc_gfp = flags;
		/*
		 * Allocation may have failed due to fragmentation.
		 * Try a lower order alloc if possible
		 */
		page = alloc_slab_page(s, alloc_gfp, node, oo);

		if (page)
			stat(s, ORDER_FALLBACK);
	}

	if (!page)
		goto out;

Why not have it do this:

	page = alloc_slab_page(s, alloc_gfp, node, oo);
	if (unlikely(!page)) {
		oo = s->min;
		alloc_gfp = flags;
		/*
		 * Allocation may have failed due to fragmentation.
		 * Try a lower order alloc if possible
		 */
		page = alloc_slab_page(s, alloc_gfp, node, oo);
		if (unlikely(!page))
			goto out;

		stat(s, ORDER_FALLBACK);
	}

And get rid of the double check for !page in the fast path.

-- Steve


> +
> +	if (kmemcheck_enabled &&
> +	    !(s->flags & (SLAB_NOTRACK | DEBUG_DEFAULT_FLAGS))) {
>  		int pages = 1 << oo_order(oo);
>  
>  		kmemcheck_alloc_shadow(page, oo_order(oo), alloc_gfp, node);
> @@ -1380,51 +1396,12 @@ static struct page *allocate_slab(struct
>  			kmemcheck_mark_unallocated_pages(page, pages);
>  	}
>  
> -	if (flags & __GFP_WAIT)
> -		local_irq_disable();
>  	if (!page)
> -		return NULL;
> +		goto out;
>  
>  	page->objects = oo_objects(oo);

--
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