Re: [PATCH v2 2/4] mm/vmalloc: add support for __GFP_NOFAIL

[Andrew Morton]

On Fri, 26 Nov 2021 11:48:46 +0100 Michal Hocko <mhocko@xxxxxxxx> wrote:

> On Mon 22-11-21 16:32:31, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@xxxxxxxx>
> > 
> > Dave Chinner has mentioned that some of the xfs code would benefit from
> > kvmalloc support for __GFP_NOFAIL because they have allocations that
> > cannot fail and they do not fit into a single page.
> > 
> > The large part of the vmalloc implementation already complies with the
> > given gfp flags so there is no work for those to be done. The area
> > and page table allocations are an exception to that. Implement a retry
> > loop for those.
> > 
> > Add a short sleep before retrying. 1 jiffy is a completely random
> > timeout. Ideally the retry would wait for an explicit event - e.g.
> > a change to the vmalloc space change if the failure was caused by
> > the space fragmentation or depletion. But there are multiple different
> > reasons to retry and this could become much more complex. Keep the retry
> > simple for now and just sleep to prevent from hogging CPUs.
> > 
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> 
> Are there still any concerns around this patch or the approach in
> general?

Well.  Like GFP_NOFAIL, every use is a sin.  But I don't think I've
ever seen a real-world report of anyone hitting GFP_NOFAIL's
theoretical issues.

I assume there will be a v3?