On Thu 03-10-19 10:00:08, Vlastimil Babka wrote: > On 10/3/19 12:32 AM, David Rientjes wrote: > > On Wed, 2 Oct 2019, Michal Hocko wrote: > > > >>>> If > >>>> hugetlb wants to stress this to the fullest extent possible, it already > >>>> appropriately uses __GFP_RETRY_MAYFAIL. > >>> > >>> Which doesn't work anymore right now, and should again after this patch. > >> > >> I didn't get to fully digest the patch Vlastimil is proposing. (Ab)using > >> __GFP_NORETRY is quite subtle but it is already in place with some > >> explanation and a reference to THPs. So while I am not really happy it > >> is at least something you can reason about. > >> > > > > It's a no-op: > > > > /* Do not loop if specifically requested */ > > if (gfp_mask & __GFP_NORETRY) > > goto nopage; > > > > /* > > * Do not retry costly high order allocations unless they are > > * __GFP_RETRY_MAYFAIL > > */ > > if (costly_order && !(gfp_mask & __GFP_RETRY_MAYFAIL)) > > goto nopage; > > > > So I'm not sure we should spend too much time discussing a hunk of a patch > > that doesn't do anything. > > I believe Michal was talking about my (ab)use of __GFP_NORETRY, where it > controls the earlier 'goto nopage' condition. That is correct. From a maintainability point of view it would be better to have only a single bailout of an optimistic compaction attempt. If we go with [1] then we have two different criterion to bail out and that is really messy and error prone. While sticking __GFP_RETRY_MAYFAIL as suggest in [1] fixes up the immediate regression in the simplest way this all really begs for a proper analysis and a _real_ fix. Can we move that direction finally, please? I would really love to conduct further testing but I haven't really heard anything to results presented so far. I have no idea whether that is even remotely resembling anything David needs for his claimed regression. [1] http://lkml.kernel.org/r/alpine.DEB.2.21.1910021556270.187014@xxxxxxxxxxxxxxxxxxxxxxxxx -- Michal Hocko SUSE Labs
