[dpdk-dev] [PATCH 9/9] memalloc: allocate memory in reverse

Burakov, Anatoly anatoly.burakov at intel.com
Tue Jul 24 12:10:11 CEST 2018


On 11-Jun-18 9:55 PM, Anatoly Burakov wrote:
> Currently, all hugepages are allocated from lower VA address to
> higher VA address, while malloc heap allocates from higher VA
> address to lower VA address. This results in heap fragmentation
> over time due to multiple reserves leaving small space below the
> allocated elements.
> 
> Fix this by allocating VA memory from the top, thereby reducing
> fragmentation and lowering overall memory usage.
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
> ---
>   lib/librte_eal/linuxapp/eal/eal_memalloc.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_eal/linuxapp/eal/eal_memalloc.c b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
> index 8c11f98c9..d35fb52c4 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_memalloc.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
> @@ -682,7 +682,8 @@ alloc_seg_walk(const struct rte_memseg_list *msl, void *arg)
>   	need = wa->n_segs;
>   
>   	/* try finding space in memseg list */
> -	cur_idx = rte_fbarray_find_next_n_free(&cur_msl->memseg_arr, 0, need);
> +	cur_idx = rte_fbarray_find_prev_n_free(&cur_msl->memseg_arr,
> +			cur_msl->memseg_arr.len - 1, need);
>   	if (cur_idx < 0)
>   		return 0;
>   	start_idx = cur_idx;
> 

Hi Thomas,

We have discovered a few regressions in virtio/vhost use cases due to 
this patch. Virtio expects to map all segments starting from 0 address, 
and this patch breaks that assumption.

Can we revert this for 18.08? It will be reintroduced in 18.11 along 
with fixes for virtio/vhost fixes to account for this change.

-- 
Thanks,
Anatoly


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