On Tue 06-08-19 20:24:03, Pankaj Suryawanshi wrote: > On Tue, 6 Aug, 2019, 1:46 AM Michal Hocko, <mhocko@xxxxxxxxxx> wrote: > > > > On Mon 05-08-19 21:04:53, Pankaj Suryawanshi wrote: > > > On Mon, Aug 5, 2019 at 5:35 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > > > > > On Mon 05-08-19 13:56:20, Vlastimil Babka wrote: > > > > > On 8/5/19 1:24 PM, Michal Hocko wrote: > > > > > >> [ 727.954355] CPU: 0 PID: 56 Comm: kworker/u8:2 Tainted: P O 4.14.65 #606 > > > > > > [...] > > > > > >> [ 728.029390] [<c034a094>] (oom_kill_process) from [<c034af24>] (out_of_memory+0x140/0x368) > > > > > >> [ 728.037569] r10:00000001 r9:c12169bc r8:00000041 r7:c121e680 r6:c1216588 r5:dd347d7c > [ 728.045392] r4:d5737080 > > > > > >> [ 728.047929] [<c034ade4>] (out_of_memory) from [<c03519ac>] (__alloc_pages_nodemask+0x1178/0x124c) > > > > > >> [ 728.056798] r7:c141e7d0 r6:c12166a4 r5:00000000 r4:00001155 > > > > > >> [ 728.062460] [<c0350834>] (__alloc_pages_nodemask) from [<c021e9d4>] (copy_process.part.5+0x114/0x1a28) > > > > > >> [ 728.071764] r10:00000000 r9:dd358000 r8:00000000 r7:c1447e08 r6:c1216588 r5:00808111 > > > > > >> [ 728.079587] r4:d1063c00 > > > > > >> [ 728.082119] [<c021e8c0>] (copy_process.part.5) from [<c0220470>] (_do_fork+0xd0/0x464) > > > > > >> [ 728.090034] r10:00000000 r9:00000000 r8:dd008400 r7:00000000 r6:c1216588 r5:d2d58ac0 > > > > > >> [ 728.097857] r4:00808111 > > > > > > > > > > > > The call trace tells that this is a fork (of a usermodhlper but that is > > > > > > not all that important. > > > > > > [...] > > > > > >> [ 728.260031] DMA free:17960kB min:16384kB low:25664kB high:29760kB active_anon:3556kB inactive_anon:0kB active_file:280kB inactive_file:28kB unevictable:0kB writepending:0kB present:458752kB managed:422896kB mlocked:0kB kernel_stack:6496kB pagetables:9904kB bounce:0kB free_pcp:348kB local_pcp:0kB free_cma:0kB > > > > > >> [ 728.287402] lowmem_reserve[]: 0 0 579 579 > > > > > > > > > > > > So this is the only usable zone and you are close to the min watermark > > > > > > which means that your system is under a serious memory pressure but not > > > > > > yet under OOM for order-0 request. The situation is not great though > > > > > > > > > > Looking at lowmem_reserve above, wonder if 579 applies here? What does > > > > > /proc/zoneinfo say? > > > > > > > > > What is lowmem_reserve[]: 0 0 579 579 ? > > > > This controls how much of memory from a lower zone you might an > > allocation request for a higher zone consume. E.g. __GFP_HIGHMEM is > > allowed to use both lowmem and highmem zones. It is preferable to use > > highmem zone because other requests are not allowed to use it. > > > > Please see __zone_watermark_ok for more details. > > > > > > > > This is GFP_KERNEL request essentially so there shouldn't be any lowmem > > > > reserve here, no? > > > > > > > > > Why only low 1G is accessible by kernel in 32-bit system ? > > > 1G ivirtual or physical memory (I have 2GB of RAM) ? virtual > > https://www.kernel.org/doc/gorman/, https://lwn.net/Articles/75174/ > > and many more articles. In very short, the 32b virtual address space > > is quite small and it has to cover both the users space and the > > kernel. That is why we do split it into 3G reserved for userspace and 1G > > for kernel. Kernel can only access its 1G portion directly everything > > else has to be mapped explicitly (e.g. while data is copied). > > Thanks Michal. > > > > > > > My system configuration is :- > > > 3G/1G - vmsplit > > > vmalloc = 480M (I think vmalloc size will set your highmem ?) > > > > No, vmalloc is part of the 1GB kernel adress space. > > I read in one article , vmalloc end is fixed if you increase vmalloc > size it decrease highmem. ? > Total = lowmem + (vmalloc + high mem) As the kernel is using vmalloc area _directly_ then it has to be a part of the kernel address space - thus reducing the lowmem. -- Michal Hocko SUSE Labs
