Re: [dpdk-dev] [PATCH] mem: don't use address hint for mapping unless requested

[Shahaf Shuler <shahafs@mellanox.com>]

Anatoly, Alejandro,

Any comments on this one?

Thursday, March 21, 2019 10:22 PM, Shahaf Shuler:
> Subject: [dpdk-dev] [PATCH] mem: don't use address hint for mapping
> unless requested
> 
> patch[1] added an address hint as starting address for 64 bit systems in case
> an explicit base virtual address was not set by the user.
> 
> The justification for such hint was to help devices that work in VA mode and
> has a address range limitation to work smoothly with the eal memory
> subsystem.
> 
> While the base address value selected may work fine for the eal initialization,
> it easily breaks when trying to register external memory using
> rte_extmem_register API.
> 
> Trying to register anonymous memory on RH x86_64 machine took several
> minutes, during them the function eal_get_virtual_area repeatedly scanned
> for a good VA candidate.
> 
> The attempt to guess which VA address will be free for mapping will always
> result in not portable, error prone code:
> * different application may use different libraries along w/ DPDK. One
>   can never guess which library was called first and how much virtual
>   memory it consumed.
> * external memory can be registered at any time in the application run
>   time.
> 
> This patch removes the default address hint and use the address returned by
> mmap.
> devices with address limitations should suggest to their users a proper base-
> virtaddr (EAL arg) to use.
> 
> Fixes: 1df21702873d ("mem: use address hint for mapping hugepages")
> Cc: stable@dpdk.org
> Cc: alejandro.lucero@netronome.com
> 
> [1] commit 1df21702873d ("mem: use address hint for mapping hugepages")
> 
> Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
> ---
>  lib/librte_eal/common/eal_common_memory.c | 22 ----------------------
>  1 file changed, 22 deletions(-)
> 
> diff --git a/lib/librte_eal/common/eal_common_memory.c
> b/lib/librte_eal/common/eal_common_memory.c
> index c9da69b164..09108f7a32 100644
> --- a/lib/librte_eal/common/eal_common_memory.c
> +++ b/lib/librte_eal/common/eal_common_memory.c
> @@ -39,23 +39,6 @@
>  static void *next_baseaddr;
>  static uint64_t system_page_sz;
> 
> -#ifdef RTE_ARCH_64
> -/*
> - * Linux kernel uses a really high address as starting address for serving
> - * mmaps calls. If there exists addressing limitations and IOVA mode is VA,
> - * this starting address is likely too high for those devices. However, it
> - * is possible to use a lower address in the process virtual address space
> - * as with 64 bits there is a lot of available space.
> - *
> - * Current known limitations are 39 or 40 bits. Setting the starting address
> - * at 4GB implies there are 508GB or 1020GB for mapping the available
> - * hugepages. This is likely enough for most systems, although a device with
> - * addressing limitations should call rte_mem_check_dma_mask for
> ensuring all
> - * memory is within supported range.
> - */
> -static uint64_t baseaddr = 0x100000000; -#endif
> -
>  void *
>  eal_get_virtual_area(void *requested_addr, size_t *size,
>  		size_t page_sz, int flags, int mmap_flags) @@ -79,11 +62,6
> @@ eal_get_virtual_area(void *requested_addr, size_t *size,
>  			rte_eal_process_type() == RTE_PROC_PRIMARY)
>  		next_baseaddr = (void *) internal_config.base_virtaddr;
> 
> -#ifdef RTE_ARCH_64
> -	if (next_baseaddr == NULL && internal_config.base_virtaddr == 0 &&
> -			rte_eal_process_type() == RTE_PROC_PRIMARY)
> -		next_baseaddr = (void *) baseaddr;
> -#endif
>  	if (requested_addr == NULL && next_baseaddr != NULL) {
>  		requested_addr = next_baseaddr;
>  		requested_addr = RTE_PTR_ALIGN(requested_addr,
> page_sz);
> --
> 2.12.0