On Thu, 20 Jul 2017, Michal Hocko wrote:
> On Wed 19-07-17 18:54:40, Hugh Dickins wrote:
> [...]
> > You probably won't welcome getting into alternatives at this late stage;
> > but after hacking around it one way or another because of its pointless
> > lockups, I lost patience with that too_many_isolated() loop a few months
> > back (on realizing the enormous number of pages that may be isolated via
> > migrate_pages(2)), and we've been running nicely since with something like:
> >
> > bool got_mutex = false;
> >
> > if (unlikely(too_many_isolated(pgdat, file, sc))) {
> > if (mutex_lock_killable(&pgdat->too_many_isolated))
> > return SWAP_CLUSTER_MAX;
> > got_mutex = true;
> > }
> > ...
> > if (got_mutex)
> > mutex_unlock(&pgdat->too_many_isolated);
> >
> > Using a mutex to provide the intended throttling, without an infinite
> > loop or an arbitrary delay; and without having to worry (as we often did)
> > about whether those numbers in too_many_isolated() are really appropriate.
> > No premature OOMs complained of yet.
> >
> > But that was on a different kernel, and there I did have to make sure
> > that PF_MEMALLOC always prevented us from nesting: I'm not certain of
> > that in the current kernel (but do remember Johannes changing the memcg
> > end to make it use PF_MEMALLOC too). I offer the preview above, to see
> > if you're interested in that alternative: if you are, then I'll go ahead
> > and make it into an actual patch against v4.13-rc.
>
> I would rather get rid of any additional locking here and my ultimate
> goal is to make throttling at the page allocator layer rather than
> inside the reclaim.
Fair enough, I'm certainly in no hurry to send the patch,
but thought it worth mentioning.
Hugh
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