Thank you for the quick reply! On Tue, Oct 22, 2019 at 1:57 PM Rafael J. Wysocki <raf...@kernel.org> wrote: > > 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.
Sorry, I don't understand this. Are you saying that, for instance, you can resume a 30 GB image on a 32 GB device, but that image could only have been created on a 64 GB device? > > 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. Again, I don't understand. Why did you make that suggestion then? > hibernate_preallocate_memory() manages to free a sufficient amount of > memory on my system every time. Unfortunately this doesn't work for me. I may have described a simple experiment: on a 4GB device, create two large processes like this: dd if=/dev/zero bs=1100M count=1 | sleep infinity & dd if=/dev/zero bs=1100M count=1 | sleep infinity & so that more than 50% of TotalMem is used for anonymous pages. Then echo disk > /sys/power/state fails with ENOMEM. Is this supposed to work? Maybe I am doing something wrong? Hibernation works before I create the dd processes. After I force some of those pages to a separate swap device, hibernation works too, so those pages aren't mlocked or anything. > > 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. I apologize if I am doing something stupid and I should know better before I waste other people's time. I have been trying to explain these issues as best as I can. I have a reproducible failure. I'll be happy to provide any additional detail. > > > 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. Sure, after we resolve the above questions. > > 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.
