On Tue, Dec 20, 2016 at 02:49:03PM +0100, Michal Hocko wrote: > From: Michal Hocko <[email protected]> > > __alloc_pages_may_oom makes sure to skip the OOM killer depending on > the allocation request. This includes lowmem requests, costly high > order requests and others. For a long time __GFP_NOFAIL acted as an > override for all those rules. This is not documented and it can be quite > surprising as well. E.g. GFP_NOFS requests are not invoking the OOM > killer but GFP_NOFS|__GFP_NOFAIL does so if we try to convert some of > the existing open coded loops around allocator to nofail request (and we > have done that in the past) then such a change would have a non trivial > side effect which is far from obvious. Note that the primary motivation > for skipping the OOM killer is to prevent from pre-mature invocation. > > The exception has been added by 82553a937f12 ("oom: invoke oom killer > for __GFP_NOFAIL"). The changelog points out that the oom killer has to > be invoked otherwise the request would be looping for ever. But this > argument is rather weak because the OOM killer doesn't really guarantee > a forward progress for those exceptional cases: > - it will hardly help to form costly order which in turn can > result in the system panic because of no oom killable task in > the end - I believe we certainly do not want to put the system > down just because there is a nasty driver asking for order-9 > page with GFP_NOFAIL not realizing all the consequences. It is > much better this request would loop for ever than the massive > system disruption > - lowmem is also highly unlikely to be freed during OOM killer > - GFP_NOFS request could trigger while there is still a lot of > memory pinned by filesystems. > > The pre-mature OOM killer is a real issue as reported by Nils Holland > kworker/u4:5 invoked oom-killer: > gfp_mask=0x2400840(GFP_NOFS|__GFP_NOFAIL), nodemask=0, order=0, > oom_score_adj=0 > kworker/u4:5 cpuset=/ mems_allowed=0 > CPU: 1 PID: 2603 Comm: kworker/u4:5 Not tainted 4.9.0-gentoo #2 > Hardware name: Hewlett-Packard Compaq 15 Notebook PC/21F7, BIOS F.22 > 08/06/2014 > Workqueue: writeback wb_workfn (flush-btrfs-1) > eff0b604 c142bcce eff0b734 00000000 eff0b634 c1163332 00000000 00000292 > eff0b634 c1431876 eff0b638 e7fb0b00 e7fa2900 e7fa2900 c1b58785 eff0b734 > eff0b678 c110795f c1043895 eff0b664 c11075c7 00000007 00000000 00000000 > Call Trace: > [<c142bcce>] dump_stack+0x47/0x69 > [<c1163332>] dump_header+0x60/0x178 > [<c1431876>] ? ___ratelimit+0x86/0xe0 > [<c110795f>] oom_kill_process+0x20f/0x3d0 > [<c1043895>] ? has_capability_noaudit+0x15/0x20 > [<c11075c7>] ? oom_badness.part.13+0xb7/0x130 > [<c1107df9>] out_of_memory+0xd9/0x260 > [<c110ba0b>] __alloc_pages_nodemask+0xbfb/0xc80 > [<c110414d>] pagecache_get_page+0xad/0x270 > [<c13664a6>] alloc_extent_buffer+0x116/0x3e0 > [<c1334a2e>] btrfs_find_create_tree_block+0xe/0x10 > [...] > Normal free:41332kB min:41368kB low:51708kB high:62048kB > active_anon:0kB inactive_anon:0kB active_file:532748kB inactive_file:44kB > unevictable:0kB writepending:24kB present:897016kB managed:836248kB > mlocked:0kB slab_reclaimable:159448kB slab_unreclaimable:69608kB > kernel_stack:1112kB pagetables:1404kB bounce:0kB free_pcp:528kB > local_pcp:340kB free_cma:0kB > lowmem_reserve[]: 0 0 21292 21292 > HighMem free:781660kB min:512kB low:34356kB high:68200kB > active_anon:234740kB inactive_anon:360kB active_file:557232kB > inactive_file:1127804kB unevictable:0kB writepending:2592kB present:2725384kB > managed:2725384kB mlocked:0kB slab_reclaimable:0kB slab_unreclaimable:0kB > kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:800kB local_pcp:608kB > free_cma:0kB > > this is a GFP_NOFS|__GFP_NOFAIL request which invokes the OOM killer > because there is clearly nothing reclaimable in the zone Normal while > there is a lot of page cache which is most probably pinned by the fs but > GFP_NOFS cannot reclaim it. > > This patch simply removes the __GFP_NOFAIL special case in order to have > a more clear semantic without surprising side effects. > > Reported-by: Nils Holland <[email protected]> > Signed-off-by: Michal Hocko <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
