We have encountered two problems with memory hotplug/hotremove in 3.0.1 -- this is a port of memory hotplug to ARM with a few small changes noted below. Neither of these occurred on a similar 2.6.38-based port we did to the same hardware. The memory is essentially 2 512M memory banks, the lower is always on, the upper is the one we are powering on and off. ARCH_POPULATES_NODE_MAP was ported to ARM and a small change was made to ensure that the movable zone could be placed exactly where desired (as movablecore= does not and must be specified on the command line -- we don't know where the movable zone must be until the kernel starts coming up). Also the upper 512M is forced to be highmem as the movable zone must come from the highest physical memory zone (of course highmem may be larger than 512M, just not smaller). 1. If highmem is set to start at exactly 512M, then all of highmem is used up when forming the movable zone. This seems to confuse the memory management subsystem (page reclaim?) because although the memory hotremove of the upper 512M succeeds, running a command that takes a pagefault after hotremove causes the system to hang: try_to_free_pages __alloc_pages_nodemask do_wp_page handle_pte_fault handle_mm_fault do_page_fault try_to_free_pages() is called repeatedly (forever), making no apparent progress. After some experimentation, I discovered that making the highmem zone at least 5M larger than the 512M movable zone appears to make the problem disappear. I can (if I don't run anything that provokes the above bug) hotplug the 512M back in, and then this problem does not occur. I've seen some discussion about very small zones causing problems. Is what we are seeing a known problem? Is there a known fix (or at least a patch we could try)? 2. Assuming the workaround we have for #1 is present, we see memory hotremove occasionally fail. This seems to (after a few seconds) cause init's state to become corrupted, provoking a panic -- sometimes (but not always) init's PC is 0. Sometimes additional (not always the same) processes also unexpectedly exit after the memory hotremove attempt. Thanks in advance for any insight you might have. Larry Bassel -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>