Date: Thu, 25 Jul 2024 18:40:31 -0400 From: Mark Johnston <markj@freebsd.org> To: Jake Freeland <jake@technologyfriends.net> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: FreeBSD hugepages Message-ID: <ZqLUX47CAUAlq7nq@nuc> In-Reply-To: <ZqLTA_tSP9dEQwil@nuc> References: <1ced4290-4a31-4218-8611-63a44c307e87@technologyfriends.net> <ZqKhP0aR0fb_f6XE@kib.kiev.ua> <35da66f9-b913-45ea-90f4-16a2fa072848@technologyfriends.net> <ZqKzCK4pHg1mrSOa@nuc> <4d4398e5-81ba-4fbd-9806-649ec70abdb4@technologyfriends.net> <ZqLTA_tSP9dEQwil@nuc>
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On Thu, Jul 25, 2024 at 06:34:43PM -0400, Mark Johnston wrote: > On Thu, Jul 25, 2024 at 04:11:22PM -0500, Jake Freeland wrote: > > On 7/25/24 15:18, Mark Johnston wrote: > > > On Thu, Jul 25, 2024 at 02:47:16PM -0500, Jake Freeland wrote: > > > > On 7/25/24 14:02, Konstantin Belousov wrote: > > > > > On Thu, Jul 25, 2024 at 01:46:17PM -0500, Jake Freeland wrote: > > > > > > Hi there, > > > > > > > > > > > > I have been steadily working on bringing Data Plane Development Kit (DPDK) > > > > > > on FreeBSD up to date with the Linux version. The most significant hurdle so > > > > > > far has been supporting concurrent DPDK processes, each with their own > > > > > > contiguous memory regions. > > > > > > > > > > > > These contiguous regions are used by DPDK as a heap for allocating DMA > > > > > > buffers and other miscellaneous resources. Retrieving the underlying memory > > > > > > and mapping these regions is currently different on Linux and FreeBSD: > > > > > > > > > > > > On Linux, hugepages are fetched from the kernel's pre-allocated hugepage > > > > > > pool and are mapped into virtual address space on DPDK initialization. Since > > > > > > the hugepages exist in a pool, multiple processes can reserve their own > > > > > > hugepages and operate concurrently. > > > > > > > > > > > > On FreeBSD, DPDK uses an in-house contigmem kernel module that reserves a > > > > > > large contiguous region of memory on load. During DPDK initialization, the > > > > > > entire region is mapped into virtual address space. This leaves no memory > > > > > > for another independent DPDK process, so only one process can operate at a > > > > > > time. > > > > > > > > > > > > I could modify the DPDK contigmem module to mimic Linux's hugepages, but I > > > > > > thought it would be better to integrate and upstream a hugepage-like > > > > > > interface directly in the FreeBSD kernel source. I am writing this email to > > > > > > see if anyone has any advice on the matter. I did not see any previous > > > > > > attempts at this in Phabriactor or the commit log, but it is possible that I > > > > > > missed it. I have read about transparent superpage promotion, but that seems > > > > > > like a different mechanism altogether. > > > > > > > > > > > > At a quick glance, the implementation seems straightforward: read some > > > > > > loader tunables, allocate persistent hugepages at boot time, and create a > > > > > > pseudo filesystem that supports creating and mapping hugepages. I could be > > > > > > underestimating the magnitude of this task, but that is why I'm asking for > > > > > > thoughts and advice :) > > > > > > > > > > > > For reference, here is Linux's documentation on hugepages: > > > > > > https://docs.kernel.org/admin-guide/mm/hugetlbpage.html > > > > > Are posix shm largepages objects enough (they were developed to support > > > > > DPDK). Look for shm_create_largepage(3). > > > > Yes, shm_create_largepage(2) looks promising, but I would like the ability > > > > to allocate these largepages at boot time when memory fragmentation as at a > > > > minimum. Perhaps a couple sysctl tunables could be added onto the > > > > vm.largepages node to specify a pagesize and allocate some number of pages > > > > at boot? > > > We could add an rc script which creates named largepage objects. This > > > can be done using the posixshmcontrol utility. That might not be early > > > enough during boot for some purposes. In that case, we could have a > > > module which creates such objects from within the kernel. This is > > > pretty straightforward to do; I wrote a dumb version of this for a > > > mips-specific project a few years ago, feel free to take code or > > > inspiration from it: https://people.freebsd.org/~markj/tlbdemo.c > > > > Looks simple enough. Thanks for the example code. > > > > > > It seems Linux had an interface similar to shm_create_largepage(2) back in > > > > v2.5, but they removed it in favor of their hugetlbfs filesystem. It would > > > > be nice to stay close to the file-backed Linux interface to maximize code > > > > sharing in userspace. It looks like the foundation for hugepages is there, > > > > but the interface for allocation and access needs to be extended. > > > POSIX shm objects have most of the properties one would want, I'd > > > expect, save the ability to access them via standard syscalls. What > > > else is missing besides the ability to reserve memory at boot time? > > > > Most notably, I would like the ability to allocate pages in a specific NUMA > > domain. > > I thought this was already supported, but it seems not... Thinking a bit more, I'm pretty sure I had just been using something like $ cpuset -n prefer:<domain> posixshmcontrol create -l 1G /largepage-1G-<domain> so didn't need an explicit NUMA configuration parameter. In C one would use cpuset_setdomain(2) instead, but that's not as convenient. So, imbuing a NUMA domain in struct shm_largepage_conf is still probably a reasonable thing to do. > It should be very easy to implement: extend shm_largepage_conf to > include a NUMA domain parameter, and specify that domain when allocating > pages for the object (in shm_largepage_dotruncate(), the > vm_page_alloc_contig() call should become a > vm_page_alloc_contig_domain() call). > > > Otherwise, in a perfect world, I'd like a unified interface for both > > Linux and FreeBSD. Linux hugepages are managed using standard system calls; > > files are mmap(2)'d into virtual address space from hugetlbfs and > > ftruncate(2)'d. > > largepage shm objects work this way as well. > > > A matching interface would not add an extra kernel > > entrypoint and even more importantly, it would ease the Linux-to-FreeBSD > > porting process for programs that use hugepages.
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