On Tue, Oct 22, 2019 at 10:09 PM Luigi Semenzato <semenz...@google.com> wrote: > > Following a thread in linux-pm > (https://marc.info/?l=linux-mm&m=157012300901871) I have some issues > that may be of general interest. > > 1. To the best of my knowledge, Linux hibernation is guaranteed to > fail if more than 1/2 of total RAM is in use (for instance, by > anonymous pages). My knowledge is based on evidence, experiments, > code inspection, the thread above, and a comment in > Documentation/swsusp.txt, copied here:
So I use it on a regular basis (i.e. every day) on a system that often has over 50% or RAM in use and it all works. I also know about other people using it on a regular basis. For all of these users, it is usable. > "Instead, we load the image into unused memory and then atomically > copy it back to it original location. This implies, of course, a > maximum image size of half the amount of memory." That isn't right any more. An image that is loaded during resume can, in fact, be larger than 50% of RAM. An image that is created during hibernation, however, cannot. > 2. There's no simple/general workaround. Rafael suggested on the > thread "Whatever doesn't fit into 50% of RAM needs to be swapped out > before hibernation". This is a good suggestion: I am actually close > to achieving this using memcgroups, but it's a fair amount of work, > and a fairly special case. Not everybody uses memcgroups, and I don't > know of other reliable ways of forcing swap from user level. I don't need to do anything like that. hibernate_preallocate_memory() manages to free a sufficient amount of memory on my system every time. > 3. A feature that works only when 1/2 of total RAM can be allocated > is, in my opinion, not usable, except possibly under special > circumstances, such as mine. Most of the available articles and > documentation do not mention this important fact (but for the excerpt > I mentioned, which is not in a prominent position). It can be used with over 1/2 of RAM allocated and that is quite easy to demonstrate. Honestly, I'm not sure what your problem is really. > Two questions then: > > A. Should the documentation be changed to reflect this fact more > clearly? I feel that the current situation is a disservice to the > user community. Propose changes. > B. Would it be worthwhile to improve the hibernation code to remove > this limitation? Is this of interest to anybody (other than me)? Again, propose specific changes.
