linux-kernel - Re: [PATCH] cma: allow concurrent cma pages allocation for multi-cma areas

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Message-ID: <5571BFBE.3070209@redhat.com>
Date:	Fri, 05 Jun 2015 08:26:54 -0700
From:	Laura Abbott <labbott@...hat.com>
To:	Weijie Yang <weijie.yang@...sung.com>, iamjoonsoo.kim@....com
CC:	mina86@...a86.com, m.szyprowski@...sung.com,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'Weijie Yang'" <weijie.yang.kh@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cma: allow concurrent cma pages allocation for multi-cma
 areas

On 06/05/2015 01:01 AM, Weijie Yang wrote:
> Currently we have to hold the single cma_mutex when alloc cma pages,
> it is ok when there is only one cma area in system.
> However, when there are several cma areas, such as in our Android smart
> phone, the single cma_mutex prevents concurrent cma page allocation.
>
> This patch removes the single cma_mutex and uses per-cma area alloc_lock,
> this allows concurrent cma pages allocation for different cma areas while
> protects access to the same pageblocks.
>
> Signed-off-by: Weijie Yang <weijie.yang@...sung.com>

Last I knew alloc_contig_range needed to be serialized which is why we
still had the global CMA mutex. https://lkml.org/lkml/2014/2/18/462

So NAK unless something has changed to allow this.

Laura

> ---
>   mm/cma.c |    6 +++---
>   mm/cma.h |    1 +
>   2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index 3a7a67b..eaf1afe 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -41,7 +41,6 @@
>
>   struct cma cma_areas[MAX_CMA_AREAS];
>   unsigned cma_area_count;
> -static DEFINE_MUTEX(cma_mutex);
>
>   phys_addr_t cma_get_base(const struct cma *cma)
>   {
> @@ -128,6 +127,7 @@ static int __init cma_activate_area(struct cma *cma)
>   	} while (--i);
>
>   	mutex_init(&cma->lock);
> +	mutex_init(&cma->alloc_lock);
>
>   #ifdef CONFIG_CMA_DEBUGFS
>   	INIT_HLIST_HEAD(&cma->mem_head);
> @@ -398,9 +398,9 @@ struct page *cma_alloc(struct cma *cma, unsigned int count, unsigned int align)
>   		mutex_unlock(&cma->lock);
>
>   		pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit);
> -		mutex_lock(&cma_mutex);
> +		mutex_lock(&cma->alloc_lock);
>   		ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA);
> -		mutex_unlock(&cma_mutex);
> +		mutex_unlock(&cma->alloc_lock);
>   		if (ret == 0) {
>   			page = pfn_to_page(pfn);
>   			break;
> diff --git a/mm/cma.h b/mm/cma.h
> index 1132d73..2084c9f 100644
> --- a/mm/cma.h
> +++ b/mm/cma.h
> @@ -7,6 +7,7 @@ struct cma {
>   	unsigned long   *bitmap;
>   	unsigned int order_per_bit; /* Order of pages represented by one bit */
>   	struct mutex    lock;
> +	struct mutex    alloc_lock;
>   #ifdef CONFIG_CMA_DEBUGFS
>   	struct hlist_head mem_head;
>   	spinlock_t mem_head_lock;
>

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