On Wed 04-04-18 09:24:06, Joonsoo Kim wrote: > 2017-09-14 22:24 GMT+09:00 Michal Hocko <mhocko@xxxxxxxxxx>: > > [Sorry for a later reply] > > > > On Wed 06-09-17 13:35:25, Joonsoo Kim wrote: > >> From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > >> > >> Freepage on ZONE_HIGHMEM doesn't work for kernel memory so it's not that > >> important to reserve. > > > > I am still not convinced this is a good idea. I do agree that reserving > > memory in both HIGHMEM and MOVABLE is just wasting memory but removing > > the reserve from the highmem as well will result that an oom victim will > > allocate from lower zones and that might have unexpected side effects. > > Looks like you are confused. > > This patch only affects the situation that ZONE_HIGHMEM and ZONE_MOVABLE is > used at the same time. In that case, before this patch, ZONE_HIGHMEM has > reserve for GFP_HIGHMEM | GFP_MOVABLE request, but, with this patch, no reserve > in ZONE_HIGHMEM for GFP_HIGHMEM | GFP_MOVABLE request. This perfectly > matchs with your hope. :) I have forgot all the details but my vague recollection is that the concern was that GFP_HIGHUSER_MOVABLE etc. wouldn't keep any reserve in the highmem zone and so emergency allocations - e.g. those during OOM will have to fallback to kernel zones and might lead to hard to predict results. Am I still confused and this will not happen after the patch? -- Michal Hocko SUSE Labs
