On 04/01/2022 14:00, Luck, Tony wrote: > [...] > Guilherme, > > Linux is indeed somewhat reluctant to hand out allocations > 2MB. :-( > > Do you really need the whole dmesg in the pstore dump? The expectation > is that systems run normally for a while. During that time console logs are > saved off to /var/log/messages. > > When the system crashes, the last part (the interesting bit!) of the console > log is lost. The purpose of pstore is to save that last bit. > > So while you could add code to ramoops to save multiple 2MB chunks, it > doesn't seem (to me) that it would add much value. > Thanks again Tony, for the interesting points. So, I partially agree with you: indeed, in a normal situation we have all messages collected by some userspace daemon, and when some issue/oops happens, we can rely on pstore to collect the latest portion of the log buffer (2M is a bunch!) and "merge" that with the previously collected portion, likely saved in a /var/log/ file. The problem is that our use case is a bit different: the idea is to rely on pstore/ramoops to collect the most information we can in a panic event, without the need of kdump. The latter is a pretty comprehensive/complete approach, but requires a bunch of memory reserved - it's a bit too much if we want just the task list, backtraces and memory state of the system, for example. And for that...we have the "panic_print" setting! There lies the issue: if I set panic_print to dump all backtraces, task info and memory state in a panic event, that information + the panic/oops and some previous relevant stuff, does it all fit in the 2M chunk? Likely so, but *if it doesn't fit*, we may lose _exactly_ the most important piece, which is the panic cause. The same way I have the "log_buf_len" tuning to determine how much size my log buffer has, I'd like to be able to effectively collect that much information using pstore/ramoops. Requiring that amount of space in an efi-pstore, for example, would be indeed really crazy! But ramoops is just a way for using some portion of the system RAM to save the log buffer, so I feel it'd be interesting to be able to properly collect full logs there, no matter the size of the logs. Of course, I'd like to see that as a setting, because the current behavior is great/enough for most of users I guess, as you pointed, and there's no need to change it by default. Let me know your thoughts and maybe others also have good opinions about that! Cheers, Guilherme
