On Fri 25-08-17 09:20:31, Joonsoo Kim wrote: > On Thu, Aug 24, 2017 at 11:41:58AM +0200, Vlastimil Babka wrote: > > On 08/24/2017 07:45 AM, js1304@xxxxxxxxx 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. When ZONE_MOVABLE is used, this problem would > > > theorectically cause to decrease usable memory for GFP_HIGHUSER_MOVABLE > > > allocation request which is mainly used for page cache and anon page > > > allocation. So, fix it. > > > > > > And, defining sysctl_lowmem_reserve_ratio array by MAX_NR_ZONES - 1 size > > > makes code complex. For example, if there is highmem system, following > > > reserve ratio is activated for *NORMAL ZONE* which would be easyily > > > misleading people. > > > > > > #ifdef CONFIG_HIGHMEM > > > 32 > > > #endif > > > > > > This patch also fix this situation by defining sysctl_lowmem_reserve_ratio > > > array by MAX_NR_ZONES and place "#ifdef" to right place. > > > > > > Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx> > > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > > > > Looks like I did that almost year ago, so definitely had to refresh my > > memory now :) > > > > Anyway now I looked more thoroughly and noticed that this change leaks > > into the reported sysctl. On a 64bit system with ZONE_MOVABLE: > > > > before the patch: > > vm.lowmem_reserve_ratio = 256 256 32 > > > > after the patch: > > vm.lowmem_reserve_ratio = 256 256 32 2147483647 > > > > So if we indeed remove HIGHMEM from protection (c.f. Michal's mail), we > > should do that differently than with the INT_MAX trick, IMHO. > > Hmm, this is already pointed by Minchan and I have answered that. > > lkml.kernel.org/r/<20170421013243.GA13966@js1304-desktop> > > If you have a better idea, please let me know. Why don't we just use 0. In fact we are reserving 0 pages... Using INT_MAX is just wrong. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
