On Wed 04-10-17 09:28:55, Pasha Tatashin wrote: > > > I am not really familiar with the trim_low_memory_range code path. I am > > not even sure we have to care about it because nobody should be walking > > pfns outside of any zone. > > According to commit comments first 4K belongs to BIOS, so I think the memory > exists but BIOS may or may not report it to Linux. So, reserve it to make > sure we never touch it. Yes and that memory should be outside of any zones, no? > > I am worried that this patch adds a code which > > is not really used and it will just stay that way for ever because > > nobody will dare to change it as it is too obscure and not explained > > very well. > > I could explain mine code better. Perhaps add more comments, and explain > when it can be removed? More explanation would be definitely helpful > > trim_low_memory_range is a good example of this. Why do we > > even reserve this range from the memory block allocator? The memory > > shouldn't be backed by any real memory and thus not in the allocator in > > the first place, no? > > > > Since it is not enforced in memblock that everything in reserved list must > be part of memory list, we can have it, and we need to make sure kernel does > not panic. Otherwise, it is very hard to detect such bugs. So, should we report such a memblock reservation API (ab)use to the log? Are you actually sure that trim_low_memory_range is doing a sane and really needed thing? In other words do we have a zone which contains this no-memory backed pfns? -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
