Re: [PATCH bpf-next 0/5] bpf: BPF specific memory allocator.

[Matthew Wilcox <willy@infradead.org>]

On Wed, Jul 06, 2022 at 10:50:34AM -0700, Alexei Starovoitov wrote:
> On Mon, Jul 04, 2022 at 09:34:23PM +0100, Matthew Wilcox wrote:
> > On Mon, Jun 27, 2022 at 12:03:08AM -0700, Christoph Hellwig wrote:
> > > I'd suggest you discuss you needs with the slab mainainers and the mm
> > > community firs.
> > > 
> > > On Wed, Jun 22, 2022 at 05:32:25PM -0700, Alexei Starovoitov wrote:
> > > > From: Alexei Starovoitov <ast@kernel.org>
> > > > 
> > > > Introduce any context BPF specific memory allocator.
> > > > 
> > > > Tracing BPF programs can attach to kprobe and fentry. Hence they
> > > > run in unknown context where calling plain kmalloc() might not be safe.
> > > > Front-end kmalloc() with per-cpu per-bucket cache of free elements.
> > > > Refill this cache asynchronously from irq_work.
> > 
> > I can't tell from your description whether a bump allocator would work
> > for you.  That is, can you tell which allocations need to persist past
> > program execution (and use kmalloc for them) and which can be freed as
> > soon as the program has finished (and can use the bump allocator)?
> > 
> > If so, we already have one for you, the page_frag allocator
> > (Documentation/vm/page_frags.rst).  It might need to be extended to meet
> > your needs, but it's certainly faster than the kmalloc allocator.
> 
> Already looked at it, and into mempool, and everything we could find.
> All 'normal' allocators sooner or later synchornously call into page_alloc,

Today it does, yes.  But it might be adaptable to your needs if only I
knew what those needs were.  For example, I assume that a BPF program
has a fairly tight limit on how much memory it can cause to be allocated.
Right?