On 2023-01-05 02:48, Ingo Molnar wrote:
* Aaron Thompson <dev@xxxxxxxxxx> wrote:For example, on an Amazon EC2 t3.micro VM (1 GB) booting via EFI: v6.2-rc2: # grep -E 'Node|spanned|present|managed' /proc/zoneinfo Node 0, zone DMA spanned 4095 present 3999 managed 3840 Node 0, zone DMA32 spanned 246652 present 245868 managed 178867 v6.2-rc2 + patch: # grep -E 'Node|spanned|present|managed' /proc/zoneinfo Node 0, zone DMA spanned 4095 present 3999 managed 3840 Node 0, zone DMA32 spanned 246652 present 245868 managed 222816 # +43,949 pages[ Note the annotation I added to the output - might be useful in the changelog too. ] So this patch adds around +17% of RAM to this 1 GB virtual system? That looks rather significant ... Thanks, Ingo
It is significant, but I wouldn't describe it as being added. I would say that the system is currently losing 17% of RAM due to a bug, and this patch fixes that bug.
The actual numbers depend on the mappings given by the EFI, so they're largely out of our control. As an example, similar VMs that I run with the OVMF EFI lose about 3%. I couldn't say for sure which is the outlier, but my point is that the specific values are not really the focus, this is just an example that shows that the issue can be encountered in the wild with real impact. I know I'll be happy to get that memory back, whether it is 3% or 17% :)
Thanks, -- Aaron
