Re: [PATCH v2 0/3] vmalloc enhancements

[Andrew Morton]

On Tue, 12 Feb 2019 13:47:24 -0500 Johannes Weiner <hannes@xxxxxxxxxxx> wrote:

> On Tue, Feb 12, 2019 at 09:56:45AM -0800, Roman Gushchin wrote:
> > The patchset contains few changes to the vmalloc code, which are
> > leading to some performance gains and code simplification.
> > 
> > Also, it exports a number of pages, used by vmalloc(),
> > in /proc/meminfo.
> > 
> > Patch (1) removes some redundancy on __vunmap().
> > Patch (2) separates memory allocation and data initialization
> >   in alloc_vmap_area()
> > Patch (3) adds vmalloc counter to /proc/meminfo.
> > 
> > v2->v1:
> >   - rebased on top of current mm tree
> >   - switch from atomic to percpu vmalloc page counter
> 
> I don't understand what prompted this change to percpu counters.
> 
> All writers already write vmap_area_lock and vmap_area_list, so it's
> not really saving much. The for_each_possible_cpu() for /proc/meminfo
> on the other hand is troublesome.

percpu_counters would fit here.  They have probably-unneeded locking
but I expect that will be acceptable.

And they address the issues with for_each_possible_cpu() avoidance, CPU
hotplug and transient negative values.