Re: [PATCH 0/6 v3] kvmalloc

[Michal Hocko <mhocko@kernel.org>]

On Tue 24-01-17 11:17:21, Alexei Starovoitov wrote:
> On Tue, Jan 24, 2017 at 04:17:52PM +0100, Michal Hocko wrote:
> > On Thu 12-01-17 16:37:11, Michal Hocko wrote:
> > > Hi,
> > > this has been previously posted as a single patch [1] but later on more
> > > built on top. It turned out that there are users who would like to have
> > > __GFP_REPEAT semantic. This is currently implemented for costly >64B
> > > requests. Doing the same for smaller requests would require to redefine
> > > __GFP_REPEAT semantic in the page allocator which is out of scope of
> > > this series.
> > > 
> > > There are many open coded kmalloc with vmalloc fallback instances in
> > > the tree.  Most of them are not careful enough or simply do not care
> > > about the underlying semantic of the kmalloc/page allocator which means
> > > that a) some vmalloc fallbacks are basically unreachable because the
> > > kmalloc part will keep retrying until it succeeds b) the page allocator
> > > can invoke a really disruptive steps like the OOM killer to move forward
> > > which doesn't sound appropriate when we consider that the vmalloc
> > > fallback is available.
> > > 
> > > As it can be seen implementing kvmalloc requires quite an intimate
> > > knowledge if the page allocator and the memory reclaim internals which
> > > strongly suggests that a helper should be implemented in the memory
> > > subsystem proper.
> > > 
> > > Most callers I could find have been converted to use the helper instead.
> > > This is patch 5. There are some more relying on __GFP_REPEAT in the
> > > networking stack which I have converted as well but considering we do
> > > not have a support for __GFP_REPEAT for requests smaller than 64kB I
> > > have marked it RFC.
> > 
> > Are there any more comments? I would really appreciate to hear from
> > networking folks before I resubmit the series.
> 
> while this patchset was baking the bpf side switched to use bpf_map_area_alloc()
> which fixes the issue with missing __GFP_NORETRY that we had to fix quickly.
> See commit d407bd25a204 ("bpf: don't trigger OOM killer under pressure with map alloc")
> it covers all kmalloc/vmalloc pairs instead of just one place as in this set.
> So please rebase and switch bpf_map_area_alloc() to use kvmalloc().

OK, will do. Thanks for the heads up.


-- 
Michal Hocko
SUSE Labs