On Mon, Aug 10, 2020 at 7:37 PM Baoquan He <bhe@xxxxxxxxxx> wrote: > > On 08/10/20 at 03:46pm, Yu Zhao wrote: > > On Mon, Aug 10, 2020 at 02:24:03PM -0700, Sonny Rao wrote: > > > We (Chrome OS) noticed recently one of our tests started failing on > > > upstream kernels while parsing /proc/zoneinfo > > > I think this patch is the cause: > > > > > > 26e7deadaae17 mm/vmstat.c: do not show lowmem reserve protection > > > information of empty zone > > > > > > Maybe our parser was being overly strict by looking for the protection > > > line, and it's not hard to fix but raised the question of whether there's > > > any ABI compatibility guarantees about these files? > > > > According to Documentation/admin-guide/sysctl/vm.rst, "Each zone has > > an array of protection pages". I'm not sure if this is the guarantee, > > but the doc should reflect the actual format. > > The current code will list all zones in one memory node, even though > that node only has one existing zone. E.g in below node 1, > it only has NORMAL zone, but we will list zone DMA, DMA32, MOVABLE, > DEVICE which are all empty zone, namely doesn't exist. So, each zone > has an array of protection pages, it should not include the nonexistent > zone. I thought nobody would check the protection line of an empty zone, > seems I was wrong. This particular parser was written as a state machine and that line was a convenient thing to look for to mark the end of each zone. AFAICT, there's no explicit documentation on the layout of that file though. > > > (Note that below /proc/zoneinfo is from an old system, protection line > is still existing for empty zone) > Node 1, zone DMA > pages free 0 > min 0 > low 0 > high 0 > spanned 0 > present 0 > managed 0 > protection: (0, 0, 61854, 61854, 61854) > Node 1, zone DMA32 > pages free 0 > min 0 > low 0 > high 0 > spanned 0 > present 0 > managed 0 > protection: (0, 0, 61854, 61854, 61854) > Node 1, zone Normal > per-node stats > nr_inactive_anon 259 > nr_active_anon 11926 > ... > nr_written 0 > nr_kernel_misc_reclaimable 0 > pages free 16206452 > pages free 16206452 > min 11280 > low 27114 > high 42948 > spanned 16777216 > present 16777216 > managed 15834637 > protection: (0, 0, 0, 0, 0) > ... > > Node 1, zone Movable > pages free 0 > min 0 > low 0 > high 0 > spanned 0 > present 0 > managed 0 > protection: (0, 0, 0, 0, 0) > Node 1, zone Device > pages free 0 > min 0 > low 0 > high 0 > spanned 0 > present 0 > managed 0 > protection: (0, 0, 0, 0, 0) > > >
