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Date: Tue, 3 Mar 2020 14:29:34 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Christoph Hellwig <hch@....de>,
Tom Lendacky <thomas.lendacky@....com>
cc: "Singh, Brijesh" <brijesh.singh@....com>,
"Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
baekhw@...gle.com,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [rfc 4/6] dma-remap: dynamically expanding atomic pools
On Sun, 1 Mar 2020, David Rientjes wrote:
> When an atomic pool becomes fully depleted because it is now relied upon
> for all non-blocking allocations through the DMA API, allow background
> expansion of each pool by a kworker.
>
> When an atomic pool has less than the default size of memory left, kick
> off a kworker to dynamically expand the pool in the background. The pool
> is doubled in size.
>
> This allows the default size to be kept quite low when one or more of the
> atomic pools is not used.
>
> Also switch over some node ids to the more appropriate NUMA_NO_NODE.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
> kernel/dma/remap.c | 79 ++++++++++++++++++++++++++++++++++------------
> 1 file changed, 58 insertions(+), 21 deletions(-)
>
> diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c
> --- a/kernel/dma/remap.c
> +++ b/kernel/dma/remap.c
> @@ -10,6 +10,7 @@
> #include <linux/genalloc.h>
> #include <linux/slab.h>
> #include <linux/vmalloc.h>
> +#include <linux/workqueue.h>
>
> struct page **dma_common_find_pages(void *cpu_addr)
> {
> @@ -104,7 +105,10 @@ static struct gen_pool *atomic_pool_dma32 __ro_after_init;
> static struct gen_pool *atomic_pool_normal __ro_after_init;
>
> #define DEFAULT_DMA_COHERENT_POOL_SIZE SZ_256K
> -static size_t atomic_pool_size __initdata = DEFAULT_DMA_COHERENT_POOL_SIZE;
> +static size_t atomic_pool_size = DEFAULT_DMA_COHERENT_POOL_SIZE;
> +
> +/* Dynamic background expansion when the atomic pool is near capacity */
> +struct work_struct atomic_pool_work;
>
> static int __init early_coherent_pool(char *p)
> {
> @@ -113,14 +117,14 @@ static int __init early_coherent_pool(char *p)
> }
> early_param("coherent_pool", early_coherent_pool);
>
> -static int __init __dma_atomic_pool_init(struct gen_pool **pool,
> - size_t pool_size, gfp_t gfp)
> +static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
> + gfp_t gfp)
> {
> - const unsigned int order = get_order(pool_size);
> const unsigned long nr_pages = pool_size >> PAGE_SHIFT;
> + const unsigned int order = get_order(pool_size);
> struct page *page;
> void *addr;
> - int ret;
> + int ret = -ENOMEM;
>
> if (dev_get_cma_area(NULL))
> page = dma_alloc_from_contiguous(NULL, nr_pages, order, false);
There's an issue here if the pool grows too large which would result in
order > MAX_ORDER-1. We can fix that by limiting order to MAX_ORDER-1 and
doing nr_pages = 1 << order.
I should also add support for trying smaller page allocations if our
preferred expansion size results in an allocation failure.
Other than that, I'll remove the RFC tag and send a refreshed series by
the end of the week unless there are other comments or suggestions to
factor in.
Thanks!
> @@ -131,38 +135,67 @@ static int __init __dma_atomic_pool_init(struct gen_pool **pool,
>
> arch_dma_prep_coherent(page, pool_size);
>
> - *pool = gen_pool_create(PAGE_SHIFT, -1);
> - if (!*pool)
> - goto free_page;
> -
> addr = dma_common_contiguous_remap(page, pool_size,
> pgprot_dmacoherent(PAGE_KERNEL),
> __builtin_return_address(0));
> if (!addr)
> - goto destroy_genpool;
> + goto free_page;
>
> - ret = gen_pool_add_virt(*pool, (unsigned long)addr, page_to_phys(page),
> - pool_size, -1);
> + ret = gen_pool_add_virt(pool, (unsigned long)addr, page_to_phys(page),
> + pool_size, NUMA_NO_NODE);
> if (ret)
> goto remove_mapping;
> - gen_pool_set_algo(*pool, gen_pool_first_fit_order_align, NULL);
>
> - pr_info("DMA: preallocated %zu KiB %pGg pool for atomic allocations\n",
> - pool_size >> 10, &gfp);
> return 0;
>
> remove_mapping:
> dma_common_free_remap(addr, pool_size);
> -destroy_genpool:
> - gen_pool_destroy(*pool);
> - *pool = NULL;
> free_page:
> if (!dma_release_from_contiguous(NULL, page, nr_pages))
> __free_pages(page, order);
> out:
> - pr_err("DMA: failed to allocate %zu KiB %pGg pool for atomic allocation\n",
> - atomic_pool_size >> 10, &gfp);
> - return -ENOMEM;
> + return ret;
> +}
> +
> +static void atomic_pool_resize(struct gen_pool *pool, gfp_t gfp)
> +{
> + if (pool && gen_pool_avail(pool) < atomic_pool_size)
> + atomic_pool_expand(pool, gen_pool_size(pool), gfp);
> +}
> +
> +static void atomic_pool_work_fn(struct work_struct *work)
> +{
> + if (IS_ENABLED(CONFIG_ZONE_DMA))
> + atomic_pool_resize(atomic_pool, GFP_DMA);
> + if (IS_ENABLED(CONFIG_ZONE_DMA32))
> + atomic_pool_resize(atomic_pool_dma32, GFP_DMA32);
> + atomic_pool_resize(atomic_pool_normal, GFP_KERNEL);
> +}
> +
> +static int __init __dma_atomic_pool_init(struct gen_pool **pool,
> + size_t pool_size, gfp_t gfp)
> +{
> + int ret;
> +
> + *pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
> + if (!*pool)
> + return -ENOMEM;
> +
> + gen_pool_set_algo(*pool, gen_pool_first_fit_order_align, NULL);
> +
> + ret = atomic_pool_expand(*pool, pool_size, gfp);
> + if (ret) {
> + gen_pool_destroy(*pool);
> + *pool = NULL;
> + pr_err("DMA: failed to allocate %zu KiB %pGg pool for atomic allocation\n",
> + atomic_pool_size >> 10, &gfp);
> + return ret;
> + }
> +
> +
> + pr_info("DMA: preallocated %zu KiB %pGg pool for atomic allocations\n",
> + pool_size >> 10, &gfp);
> + return 0;
> }
>
> static int __init dma_atomic_pool_init(void)
> @@ -170,6 +203,8 @@ static int __init dma_atomic_pool_init(void)
> int ret = 0;
> int err;
>
> + INIT_WORK(&atomic_pool_work, atomic_pool_work_fn);
> +
> ret = __dma_atomic_pool_init(&atomic_pool_normal, atomic_pool_size,
> GFP_KERNEL);
> if (IS_ENABLED(CONFIG_ZONE_DMA)) {
> @@ -231,6 +266,8 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
> ptr = (void *)val;
> memset(ptr, 0, size);
> }
> + if (gen_pool_avail(pool) < atomic_pool_size)
> + schedule_work(&atomic_pool_work);
>
> return ptr;
> }
>
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