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

Shahaf Shuler shahafs at mellanox.com
Thu Mar 21 21:21:56 CET 2019

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

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 at dpdk.org
Cc: alejandro.lucero at netronome.com

[1] commit 1df21702873d ("mem: use address hint for mapping hugepages")

Signed-off-by: Shahaf Shuler <shahafs at 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;
 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;
 	if (requested_addr == NULL && next_baseaddr != NULL) {
 		requested_addr = next_baseaddr;
 		requested_addr = RTE_PTR_ALIGN(requested_addr, page_sz);

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