Date: Thu, 25 Jul 2024 22:02:23 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Jake Freeland <jake@technologyfriends.net> Cc: freebsd-hackers@freebsd.org Subject: Re: FreeBSD hugepages Message-ID: <ZqKhP0aR0fb_f6XE@kib.kiev.ua> In-Reply-To: <1ced4290-4a31-4218-8611-63a44c307e87@technologyfriends.net> References: <1ced4290-4a31-4218-8611-63a44c307e87@technologyfriends.net>
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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).
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