On 10/24/2013 05:51 AM, Olav Haugan wrote: > I am trying to use zram in very low memory conditions and I am having > some issues. zram is in the reclaim path. So if the system is very low > on memory the system is trying to reclaim pages by swapping out (in this > case to zram). However, since we are very low on memory zram fails to > get a page from zsmalloc and thus zram fails to store the page. We get > into a cycle where the system is low on memory so it tries to swap out > to get more memory but swap out fails because there is not enough memory > in the system! The major problem I am seeing is that there does not seem > to be a way for zram to tell the upper layers to stop swapping out > because the swap device is essentially "full" (since there is no more > memory available for zram pages). Has anyone thought about this issue > already and have ideas how to solve this or am I missing something and I > should not be seeing this issue? > The same question as Luigi "What do you want the system to do at this point?" If swap fails then OOM killer will be triggered, I don't think this will be a issue. By the way, could you take a try with zswap? Which can write pages to real swap device if compressed pool is full. > I am also seeing a couple other issues that I was wondering whether > folks have already thought about: > > 1) The size of a swap device is statically computed when the swap device > is turned on (nr_swap_pages). The size of zram swap device is dynamic > since we are compressing the pages and thus the swap subsystem thinks > that the zram swap device is full when it is not really full. Any > plans/thoughts about the possibility of being able to update the size > and/or the # of available pages in a swap device on the fly? > > 2) zsmalloc fails when the page allocated is at physical address 0 (pfn AFAIK, this will never happen. > = 0) since the handle returned from zsmalloc is encoded as (<PFN>, > <obj_idx>) and thus the resulting handle will be 0 (since obj_idx starts > at 0). zs_malloc returns the handle but does not distinguish between a > valid handle of 0 and a failure to allocate. A possible solution to this > would be to start the obj_idx at 1. Is this feasible? > > Thanks, > > Olav Haugan > -- Regards, -Bob -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>