On Tue, Jun 04, 2019 at 02:28:06PM +0200, Michal Hocko wrote: > On Thu 30-05-19 11:42:29, Minchan Kim wrote: > > On Tue, May 28, 2019 at 05:14:07PM +0200, Michal Hocko wrote: > > > [Cc Pankaj Suryawanshi who has reported a similar problem > > > http://lkml.kernel.org/r/SG2PR02MB309806967AE91179CAFEC34BE84B0@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx] > > > > > > On Fri 24-05-19 16:11:14, Minchan Kim wrote: > > > > There was below bugreport from Wu Fangsuo. > > > > > > > > 7200 [ 680.491097] c4 7125 (syz-executor) page:ffffffbf02f33b40 count:86 mapcount:84 mapping:ffffffc08fa7a810 index:0x24 > > > > 7201 [ 680.531186] c4 7125 (syz-executor) flags: 0x19040c(referenced|uptodate|arch_1|mappedtodisk|unevictable|mlocked) > > > > 7202 [ 680.544987] c0 7125 (syz-executor) raw: 000000000019040c ffffffc08fa7a810 0000000000000024 0000005600000053 > > > > 7203 [ 680.556162] c0 7125 (syz-executor) raw: ffffffc009b05b20 ffffffc009b05b20 0000000000000000 ffffffc09bf3ee80 > > > > 7204 [ 680.566860] c0 7125 (syz-executor) page dumped because: VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page)) > > > > 7205 [ 680.578038] c0 7125 (syz-executor) page->mem_cgroup:ffffffc09bf3ee80 > > > > 7206 [ 680.585467] c0 7125 (syz-executor) ------------[ cut here ]------------ > > > > 7207 [ 680.592466] c0 7125 (syz-executor) kernel BUG at /home/build/farmland/adroid9.0/kernel/linux/mm/vmscan.c:1350! > > > > 7223 [ 680.603663] c0 7125 (syz-executor) Internal error: Oops - BUG: 0 [#1] PREEMPT SMP > > > > 7224 [ 680.611436] c0 7125 (syz-executor) Modules linked in: > > > > 7225 [ 680.616769] c0 7125 (syz-executor) CPU: 0 PID: 7125 Comm: syz-executor Tainted: G S 4.14.81 #3 > > > > 7226 [ 680.626826] c0 7125 (syz-executor) Hardware name: ASR AQUILAC EVB (DT) > > > > 7227 [ 680.633623] c0 7125 (syz-executor) task: ffffffc00a54cd00 task.stack: ffffffc009b00000 > > > > 7228 [ 680.641917] c0 7125 (syz-executor) PC is at shrink_page_list+0x1998/0x3240 > > > > 7229 [ 680.649144] c0 7125 (syz-executor) LR is at shrink_page_list+0x1998/0x3240 > > > > 7230 [ 680.656303] c0 7125 (syz-executor) pc : [<ffffff90083a2158>] lr : [<ffffff90083a2158>] pstate: 60400045 > > > > 7231 [ 680.666086] c0 7125 (syz-executor) sp : ffffffc009b05940 > > > > .. > > > > 7342 [ 681.671308] c0 7125 (syz-executor) [<ffffff90083a2158>] shrink_page_list+0x1998/0x3240 > > > > 7343 [ 681.679567] c0 7125 (syz-executor) [<ffffff90083a3dc0>] reclaim_clean_pages_from_list+0x3c0/0x4f0 > > > > 7344 [ 681.688793] c0 7125 (syz-executor) [<ffffff900837ed64>] alloc_contig_range+0x3bc/0x650 > > > > 7347 [ 681.717421] c0 7125 (syz-executor) [<ffffff90084925cc>] cma_alloc+0x214/0x668 > > > > 7348 [ 681.724892] c0 7125 (syz-executor) [<ffffff90091e4d78>] ion_cma_allocate+0x98/0x1d8 > > > > 7349 [ 681.732872] c0 7125 (syz-executor) [<ffffff90091e0b20>] ion_alloc+0x200/0x7e0 > > > > 7350 [ 681.740302] c0 7125 (syz-executor) [<ffffff90091e154c>] ion_ioctl+0x18c/0x378 > > > > 7351 [ 681.747738] c0 7125 (syz-executor) [<ffffff90084c6824>] do_vfs_ioctl+0x17c/0x1780 > > > > 7352 [ 681.755514] c0 7125 (syz-executor) [<ffffff90084c7ed4>] SyS_ioctl+0xac/0xc0 > > > > > > > > Wu found it's due to [1]. Before that, unevictable page goes to cull_mlocked > > > > routine so that it couldn't reach the VM_BUG_ON_PAGE line. > > > > > > > > To fix the issue, this patch filter out unevictable LRU pages > > > > from the reclaim_clean_pages_from_list in CMA. > > > > > > The changelog is rather modest on details and I have to confess I have > > > little bit hard time to understand it. E.g. why do not we need to handle > > > the regular reclaim path? > > > > No need to pass unevictable pages into regular reclaim patch if we are > > able to know in advance. > > I am sorry to be dense here. So what is the difference in the CMA path? > Am I right that the pfn walk (CMA) rather than LRU isolation (reclaim) > is the key differentiator? Yes. We could isolate unevictable LRU pages from the pfn waker to migrate and could discard clean file-backed pages to reduce migration latency in CMA path.
