On 2/15/22 10:46 AM, Alistair Popple wrote: > Anshuman Khandual <anshuman.khandual@xxxxxxx> writes: > >> Hi Alistair, >> >> On 2/15/22 8:28 AM, Alistair Popple wrote: >>> ZONE_MOVABLE uses the remaining memory in each node. It's starting pfn >>> is also aligned to MAX_ORDER_NR_PAGES. It is possible for the remaining >>> memory in a node to be less than MAX_ORDER_NR_PAGES, meaning there is >>> not enough room for ZONE_MOVABLE on that node. >> >> How plausible is this scenario on normal systems ? > > Probably not very. I happened to run into this on my development/test x86 VM > which has 8GB and was booted with `numa=fake=4 kernelcore=60%` but in theory I > guess any system that has a node with less than MAX_ORDER_NR_PAGES left over for > ZONE_MOVABLE may be susceptible. > > This was the RAM map: > > [ 0.000000] BIOS-provided physical RAM map: > [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable > [ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved > [ 0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved > [ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000007ffddfff] usable > [ 0.000000] BIOS-e820: [mem 0x000000007ffde000-0x000000007fffffff] reserved > [ 0.000000] BIOS-e820: [mem 0x00000000b0000000-0x00000000bfffffff] reserved > [ 0.000000] BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved > [ 0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved > [ 0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved > [ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000027fffffff] usable > > [...] > > [ 0.065897] Early memory node ranges > [ 0.065898] node 0: [mem 0x0000000000001000-0x000000000009efff] > [ 0.065900] node 0: [mem 0x0000000000100000-0x000000007ffddfff] > [ 0.065902] node 1: [mem 0x0000000100000000-0x000000017fffffff] > [ 0.065904] node 2: [mem 0x0000000180000000-0x00000001ffffffff] > [ 0.065906] node 3: [mem 0x0000000200000000-0x000000027fffffff] > > Note the reserved range from 0x000000007ffde000 to 0x000000007fffffff resulting > in node-0 ending at 0x000000007ffddfff. > >> Should not the node always contain MAX_ORDER_NR_PAGES aligned pages ? Also all >> zones which get created from that node should also be MAX_ORDER_NR_PAGES >> aligned ? > > I'm not sure why that would be case given page size and MAX_ORDER_NR_PAGES can > be set via a kernel configuration parameter. Obviously it wasn't the case here I assumed that in general that would be the case. > or this situation would not arise. That said I don't know this code well, and > this was where I decided to stop shaving this yak so it's possible there is an > even deeper underlying issue. > > Either way I don't *think* the fix should introduce any problems as it shouldn't > do anything unless you were going to hit this issue anyway (which took sometime > to track down as the cause wasn't obvious). Fair enough. > >> I am just curious how a node could end up being like this. > > - Anshuman >
