On 19-Mar-18 5:30 PM, Olivier Matz wrote:
Hi Anatoly,
On Sat, Mar 03, 2018 at 01:45:48PM +0000, Anatoly Burakov wrote:
This patchset introduces dynamic memory allocation for DPDK (aka memory
hotplug). Based upon RFC submitted in December [1].
Dependencies (to be applied in specified order):
- IPC bugfixes patchset [2]
- IPC improvements patchset [3]
- IPC asynchronous request API patch [4]
- Function to return number of sockets [5]
Deprecation notices relevant to this patchset:
- General outline of memory hotplug changes [6]
- EAL NUMA node count changes [7]
The vast majority of changes are in the EAL and malloc, the external API
disruption is minimal: a new set of API's are added for contiguous memory
allocation for rte_memzone, and a few API additions in rte_memory due to
switch to memseg_lists as opposed to memsegs. Every other API change is
internal to EAL, and all of the memory allocation/freeing is handled
through rte_malloc, with no externally visible API changes.
Quick outline of all changes done as part of this patchset:
* Malloc heap adjusted to handle holes in address space
* Single memseg list replaced by multiple memseg lists
* VA space for hugepages is preallocated in advance
* Added alloc/free for pages happening as needed on rte_malloc/rte_free
* Added contiguous memory allocation API's for rte_memzone
* Integrated Pawel Wodkowski's patch for registering/unregistering memory
with VFIO [8]
* Callbacks for registering memory allocations
* Multiprocess support done via DPDK IPC introduced in 18.02
The biggest difference is a "memseg" now represents a single page (as opposed to
being a big contiguous block of pages). As a consequence, both memzones and
malloc elements are no longer guaranteed to be physically contiguous, unless
the user asks for it at reserve time. To preserve whatever functionality that
was dependent on previous behavior, a legacy memory option is also provided,
however it is expected (or perhaps vainly hoped) to be temporary solution.
Why multiple memseg lists instead of one? Since memseg is a single page now,
the list of memsegs will get quite big, and we need to locate pages somehow
when we allocate and free them. We could of course just walk the list and
allocate one contiguous chunk of VA space for memsegs, but this
implementation uses separate lists instead in order to speed up many
operations with memseg lists.
For v1, the following limitations are present:
- FreeBSD does not even compile, let alone run
- No 32-bit support
- There are some minor quality-of-life improvements planned that aren't
ready yet and will be part of v2
- VFIO support is only smoke-tested (but is expected to work), VFIO support
with secondary processes is not tested; work is ongoing to validate VFIO
for all use cases
- Dynamic mapping/unmapping memory with VFIO is not supported in sPAPR
IOMMU mode - help from sPAPR maintainers requested
Nevertheless, this patchset should be testable under 64-bit Linux, and
should work for all use cases bar those mentioned above.
[1] http://dpdk.org/dev/patchwork/bundle/aburakov/Memory_RFC/
[2] http://dpdk.org/dev/patchwork/bundle/aburakov/IPC_Fixes/
[3] http://dpdk.org/dev/patchwork/bundle/aburakov/IPC_Improvements/
[4] http://dpdk.org/dev/patchwork/bundle/aburakov/IPC_Async_Request/
[5] http://dpdk.org/dev/patchwork/bundle/aburakov/Num_Sockets/
[6] http://dpdk.org/dev/patchwork/patch/34002/
[7] http://dpdk.org/dev/patchwork/patch/33853/
[8] http://dpdk.org/dev/patchwork/patch/24484/
I did a quick pass on your patches (unfortunately, I don't have
the time to really dive in it).
I have few questions/comments:
- This is really a big patchset. Thank you for working on this topic.
I'll try to test our application with it as soon as possible.
- I see from patch 17 that it is possible that rte_malloc() expands
the heap by requesting more memory to the OS? Did I understand well?
Today, a good property of rte_malloc() compared to malloc() is that
it won't interrupt the process (the worst case is a spinlock). This
is appreciable on a dataplane core. Will it change?
Hi Olivier,
Not sure what you mean by "interrupt the process". The new rte_malloc
will _mostly_ work just like the old one. There are now two levels of
locks: the heap lock, and the system allocation lock. If your rte_malloc
call requests amount of memory that can be satisfied by already
allocated memory, then only the heap lock is engaged - or, to put it in
other words, things work as before.
When you *don't* have enough memory allocated, previously rte_malloc
would just fail. Now, it instead will lock the second lock and try to
allocate more memory from the system. This requires IPC (to ensure all
processes have allocated/freed the same memory), so this will take way
longer (timeout is set to wait up to 5 seconds, although under normal
circumstances it's taking a lot less - depending on how many processes
you have running, but generally under 100ms), and will block other
system allocations (i.e. if another rte_malloc call on another heap is
trying to request more memory from the system).
So, in short - you can't allocate from the same heap in parallel (same
as before), and you can't have parallel system memory allocation
requests (regardless of from which heap it comes from). The latter
*only* applies to system memory allocations - that is, if one heap is
allocating system memory while another heap receives allocation request
*and is able to satisfy it from already allocated memory*, it will not
block, because the second lock is never engaged.
- It's not a big issue, but I have the feeling that the "const" statement
is often forgotten in the patchset. I think it is helpful for both
optimization, documentation and to detect bugs that modifies/free
something that should not.
Generally, if things aren't const, they aren't for a reason :) I made
things const by default and removed constness once i needed to. However,
there may have been a few places where i changed the code around but
forgot to put constness back. I'll look into it.
Thanks for your reviews!
I'm sending some other dummy comments as replies to patches.
Thanks,
Olivier
--
Thanks,
Anatoly
