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?
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 = 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 -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
