On Thu, Oct 24, 2013 at 5:51 AM, Olav Haugan <ohaugan@xxxxxxxxxxxxxx> 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? I agree with Luigi and Bob. zram's size is based on how many free memory you expect to use for zram. In my test, the compression ratio is about 1:4, of course the working sets may be different with yours. Further more, may be you can modify vm_swap_full() to let kernel free swap_entry aggressively. > 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 majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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>